Some of my shastas just started blooming a few weeks ago. While some of my others have been blooming for months. This is just a guess but maybe the one plant is older than the other. An older plant usually will bloom before a younger plant. I would say just give it some time if you notice something eating at the leaves then I would look closer at it.

Ps shasta daisy is my favorite :D

jen,
i have had your experience w/ a number of different plants, and this might sound weird to you, but I have developed an anthropomophic theory. The bigger, more robust, more flowering plant is the big bully sibling who keeps his sibling down,or is the successful one that the younger sibling feels unable to equal. I can account for it in no other way. Same soil, same exposure, purchased and planted at same time; one's a bully; one's a wimp.

best,
mindy

Give it another year. Some individual perennials are slow to mature. Some of my columbines are still small after 2 years and some from the same cell pack are large. And 3 of my baptisia sulked for 3 years before exploding in growth (and bloom) this year where 2 siblings are still waiting to develop.

That's part of the fun of perennials. Some of them just sit and sit and sit, then BLAM, they explode on you for years.

By the same token. 3/4 of my dependable Black-Eyed Susans just didn't come up at all this year. You never know what is going to happen.