The most important question left is how much watering the spot will get. Many shade perennial tolerate clay but fewer shade plants are drought tolerant.

My absolute favorite plant for dry shade is a perennial foxglove called "Spanish Peaks," (Digitalis thapsi) which is really tough and has abundant pink flowers that bloom all summer. It doesn't seem to care what kind of soil it's in and does well in clay. It doesn't like too much water.

A related species, Digitalis obscura, is similar but with orange flowers. Though most foxgloves are biannual, both of these are TRUE perennials that come back reliably if they're not too wet.

In my experience many types of Columbine (Aquilegia) are tolerant of clay and shade. They tend to die after 3-5 years but have already re-seeded by then.

I have grown Ajuga reptans in clay soil and it spreads happily; it likes a little more water but if dry it will only slow down - not stop. It makes a great low-growing carpet that surrounds but does not compete with the larger plants because it's too short (about 2-3 inches tall), so you won't mind it's spreading - and it makes a for good color contrast with with many other plants because of its dark leaves.

Fritillaria meleagris is a cute and interesting-looking spring bulb that likes part shade but not deep shade. It likes lots of water.

Dafodills also manage clay soils fairly well - at least much better than tulips do.

Grape hyacinths (Muscari) will grow rampant in sun, sand, clay, shade - wherever you put 'em.

Bishops weed (Aegopodium podagraria) also grows wherever you put it - but it spreads VERY aggressively so isn't recommended unless it's confined in a barrier or you don't mind if it consumes the entire available space.

Lilly of the Valley (Convallaria majalis) tolerates shade and clay. Also a vigorous spreader.

Obedient plant (Physostegia virginiana), another unruly spreader, does fine in clay in my experience. It likes it wet. Sometimes listed as a full-sun or part-sun plant, it will also adapt and do fine in shade, and prefers shade in drier climates.

Many coral bells (Huchera) tolerate clay and shade.

I'll leave other suggestions to other gardeners - there are definitely many other options.

IMHO.. how it is planted.. and watered ... is the only limiting factor in what can be grown on a clay soil ...

for e.g. .... though hosta like a lot of water... they do not like to stand in stagnant water ... so if you dig a hole and create a water retaining cauldron... your hosta may not end up happy ....

ken

One of my favorites for a shady site with or without clay is a nice low ground cover called hepatica, either round- or sharp-lobed species. They bloom early in the spring in white, pink or light blue. There is a variety that is called cobalt blue that I'm trying to get my hands on now.

In the shade here in Virginia, in dry, rock hard clay, I have Lamiums and Hellebores thriving. They get watered occasionally, but are heavily mulched. Even the deer leave them alone.

My garden soil is rocky clay & I've just lasagna layered right over it planting these plants (without repeating what others have listed)

-golden creeping Jenny - Lysimachia
-lungwort - Pulmonaria
-shasta daisy, older cultivars
-forget me not (biennial)
-wild sweet William
-Heuchera 'Firefly'
-hardy wild ginger - Asarum
-hardy bigroot - Geranium macrorrhizum
-Dusky Cranesbill (mourning widow) - Geranium phaeum
-other hardy geraniums - think it's G. x oxon... bloomed all summer - cut it back several times thinking it was done & it bloomed again)
-Darmera peltata - Indian rhubarb
-hardy ferns esp varieties native in your area
-hardy fuchsia
-Meconopsis Cambrica - Welsh Poppy
-bee balm - Monarda (flops in shade, but still blooms for me & looks great next to daisy for later summer/fall color, so they can flop together near hydrangea, rhodendron, & crocosmia 'Lucifer')
-Japanese anemone for fall color!
-Brunnera - species, not the fancy white leaved types
-monkey flower - Mimulus
-Bergenia
-sweet flag - Acorus (grows in heavy clay soils)
-Carex 'Ice Dance' - variegated grass
-Columbine
-Ligularia
-Astilbe - loves rich soil, so do give it compost/manures, etc.
-Persicaria virginiana 'Variegata' (Tovara virginiana 'Variegata')
-Vinca major (larger leaves than the minor)
-sweet woodruff
-Carex, brown (not sure the variety I have)
-daylily (though less blooms in shade)
-Miller's crimson Japanese primrose
-English primrose 'wanda' - fast growing spreader, divide every few years to keep it happy (I just take chunks out to give to other gardeners & call it good)
-Euphorbia amygdaloides var. robbiae - Robb's Spurge
-plants native to your area should also do well (I have red huckleberry, fringecup (Tellima), piggyback plant, Indian plum, low oregon grape, red currant, & various ferns doing well on the far right side in the pic below.

Mid July pic of garden planted in late March on clay soil (my manure makers: chicken, duck & rabbit coops in the background)
Most of what you see was winter sown, divisions my other gardens, or from plant swaps & just took off in our prepared soil. Composted manure + bedding is awesome!
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Be sure to remind her to use mulch to help the plants not dry out in summer.

I would definitely add Astrantia to the list...I've found that they LOVE my heavy clay soil and seem to thrive in all levels of light (except full sun). Oxalis seem to do well, as do Rodgersia...but Rodgersia do like A LOT of moisture during the growing season.Astilboides would do well, as would Darmera...again, though, they like fairly moist soil. Here are a few of the Astrantias I grew this year (for the first time!)

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Astrantia 'Abbey Road'

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Astrantia 'Roma'

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Astrantia 'Ruby Wedding'

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Astrantia maxima

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Astrantia 'Star of Beauty'

Here is a link that might be useful: My Blog

Wow, thanks so much everybody!
I don't think I was thinking about the fact that there could be more kinds of clay soil than one, but I know it will be amended and mulched.
The astrantias are really nice-looking and I'm not sure why I always pass them up when I see them in catalogues.
Corrine, thanks for the pic- I love the crocosmias (I think I've got the right plant) overarching :)
Kimka, I also love Hepatarica (and anemonellas)and just saw Jeffersonia as well and desperately want.

Crocosmia 'Lucifer' is the arching one in that pic. Seems to transplant here better if I have a large chunk of a division with roots rather than dried out corms from a swap. The dried out ones don't ever grow for me especially if transplanted in fall. All of my spring moved plants have done well & even bloomed!

Now that winter is almost here the evergreens are shining bright & the Carex 'Ice Dance' is the star of the show & they're barely visible when the hosta are out. Heuchera are also nearly evergreen in my climate.