lisa b,

Winter is a great time to plant a tree in Alabama! Fall is the best time, but winter is good too, as long as the ground isn't frozen when you plant (it rarely is here). I've attached a link below. The link is for south Alabama, but has some useful tips for how to plant, things to consider when selecting a tree, etc.

Here is a link that might be useful: planting trees in winter

here is another link

Here is a link that might be useful: another link

Some suggestions are magnolia grandiflora which are beautiful but VERY slow growing trees. I would suggest a willow oak (quercus phellos) which grows quickly, has small leaves and small acorns and grows quickly. They make beautiful trees. See the link.

Here is a link that might be useful: Willow Oak

I'd like to suggest that you contact the Alabama Urban Forest Association (AUFA) and/or your local extension office. You might be able to find an expert to come and help with the logistics of tree selection and planting.

For AUFA, use their contact information for assistance.

Here is a link that might be useful: Click here for AUFA

i think a tree with spring flowers would be a nice choice as a memorial. the spring show would be something to catch the eye of the onlookers and bring to mind the individual you are remembering.
one of my favorite native trees is chionanthus virginicus ( grancy greybeard or american fringe tree).
here is mine. they don't get huge, though; around 20' or so.
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The grancy graybeard is not longlived; it also is prone to rot and ant infestation.

A classic shade tree with no root problems for those doing the lawn maintenance is the ghinkgo biloba, and only choose the male not the female. That would be my top choice.

Another one would be an ornamental cherry, like those found in Washington DC, able to take the cold and also give a gorgeous display in the spring. A bonus for putting in such a tree would be the option of expanding this in the future with other memorial trees, to have a lengthy promenade along the drive or property borders.

I believe very much in memorial plantings. One of my favorite such plantings was a camellia japonica "Purple Dawn" which I planted in memory of my father. It was a sad day when I sold my house and this camellia was too large to take with me. Here at our new house, I have a "Pink Perfection" planted in his memory. Camellias are very hardy.

short-lived, rot and ant infestation?
i don't think so. never had those problems with mine and longevity is a relative term. certainly not to be as expected with something like an oak but not just a few years either. they are native and are practically pest-free from my experience.
i figure she has already made her selection by now but information such as that is anecdotal, at best.
ornamental cherry would be a shorter-lived selection for our region (heat tolerance rather than cold and expected life of around 20 years) since it is subject to numerous pests and disease problems.

Jeff-al, yes, I was giving my anecdotal personal experience with the tree which was in my yard at MoccasinLanding here in Mobile. I lived on the bank of a bayou and had a lot of trouble with the ants residing in the forked main trunk of the tree. It eventually caused half of the tree to die, and it looked really ugly after that.

And of course, it set my opinion of that kind of tree, to be right up there with the mimosa as a tree to avoid intentionally growing. Plants behave differently in different climates, for sure.