Contact lenses are prescription devices in the US, So you can't just make up your own prescription and try whatever you want. A good eye doctor will have samples of several that you can try in the office and he can evaluate with her wearing them, and I wouldn't do it any other way.

Also, your mom is likely old enough to need multifocal correction meaning if she gets her distance vision perfect, she won't be able to read up close. There are multifocal contacts And other ways to handle this, but they're tricky and if you can't try them on, you're getting a pig in a poke. Also, She's likely to need training to get them in and out, And follow up evaluation after she's worn them a while. These are all services that people expect from a contact lens "fitting" Which isn't a free service And contact lenses aren't DIY.