Last year, age 56, I started riding again after a long time off (maybe 15 years). I chose a step through ladies Giant Suede with 7 gears. Have ridden about 1500 miles on it and still love it. I did trade the riser handlebars for tourist type/North Road style because my wrists and forearms bothered me on longer rides (10 miles +). Highly recommend that swept back handlebar option. I'm 5' 5 1/2" and have my seat all the way up as high as it will go. Don't know how it would suit someone 5' tall.

I also test rode a Giant Simple (cruiser) and a Trek Pure. Loved them too. The Suede and Pure come in hub gears too for people who don't want to bother with shifting so much. Hope your mom finds something she loves. Remember that gears also work for windy places and not just hilly ones.