If she were coming to stay for a long time I'd take her with me to buy a chair but she's just going to be here for a couple of weeks. I don't want to spend one of those weeks furniture shopping and having her make do with something that isn't comfortable.
She's about 5'6" so I think a standard size chair will work. Also, she's pretty nimble -- she just needs a little extra help getting up.
These chairs are looking like a pretty good option. I think I'll go have a look at some!