Hi,
I just bought my dad (he is 76 today actually) his first starter kit for Christmas. Although he was open to the idea, and went with me to the vape shop to "pick a flavor" that they had for free to try. And also I let him try my istick so he can tell the difference when you can adjust the voltage. He really enjoyed the difference of changing the voltage to suit his needs/tastes. He ended up getting some cigar flavor, and he liked the shape of the ego batteries, and not the shape/size of the istick. So he left with two spinner ego twist (more cigarette feel for him he said, and he could easily twist the bottom for voltage needs, and no he can't read the numbers, he just twists and puffed until he found what level he liked), a ce5 clearomizer with bvc coils, and two bottles of juice with the flavors he tried and liked. He wanted two spinners because although they last about 10 -15 hours on one charge, he still felt he needed a backup.
If your mom is willing to go with you to the vape shop, that would be a good starting point. As the people at the vape shop I took my dad to were super friendly and helpful. If not, or you want it to be a surprise, I would go with something like a spinner which was easy for my dad to use. As far as juice, that is personal taste, and everyone is different. Although my dad liked the cigar flavors, my nephew liked a watermelon/banana blend and did not want the tobacco flavoring at all. You could try a sample pack of different flavors for her to choose from. Also, perhaps someone else could comment on the mg of nic, but it depends on her smoking habits, not just what she uses. (How often she smokes cigs in a day).