I used zenni optical online. You can upload a picture and 'try on' the frames. Then enter the info from your rx. Very inexpensive. I've used them twice with no problems whatsoever.
I used Warby Parker. They'll send you five pairs to try on; you decide which one you like, mail them all back, and they send you the prescription glasses. I don't know if they would necessarily be your mom's style though (unless your mom is trendier than mine).