I would simply add to all the great suggestions here that at any age but particularly over 50 with some range of motion issues etc it's all about the fit. Whatever she gets it must fit her.

I often say you're buying two things when you get a bike:
the frame
the bike shop

You're stuck with the frame. If you get a good one it's a lifetime bike. She may swap everything else after miles and miles of happy riding. The frame is the "soul" of a bike and determines fit and ride feel.

The shop! Her LBS will be her mentor when you are away, her coach, cheering section and guru. Find a shop that does not talk over her or down to her.

Instead of plugging in this bike or that and links to bikes I'd visit her, do some bike shopping and Mom/Daughter bonding time, find an LBS and tell them "she wants to do this" and try their bikes in that range!!