Black tea has the most caffeine (but still much less than coffee).

On that webpage, you can select more specific types.

Green tea is usually considered the “most healthy” even though they all are very healthy.
Earl Grey tea is very popular, especially in Britain. It is black tea with bergamot orange oil.

You should look up what good steeping times are. (I know you may already know this.) Many people leave the teabag in for too long, making it bitter. I drink green tea all the time and 2 and a half minutes are perfectly fine. Black teas need more time.

Here is an article that also explains the nutrition of tea:

I’m pretty sure all tea is healthier than coffee.

————————-
Anyway, you should include more than one type of tea. This way, your mom can decide what she likes best. Green, black, Earl Grey (unless she doesn’t like citrus flavors or has some allergy to bergamot oranges)…those are the most common.

There are also “herbal” teas. These don’t come from tea plants (or “Camellia sinensis”), but are also usually very healthy. The first link I gave includes some common herbal teas. Most don’t have caffeine, so it might not be what your mom is looking for.

Good luck. (betcha didn’t know that tea was like a magic health drink did you?)