Umm...so many machines, so many price ranges. We would need more information to make suggestions.
1. has grandma sewn before? What kind of machine did she use? What types of things does she like to sew?
2. Is grandma tech savy? Does she use a fancy cell phone or computer...most machines now have a least some computer like features
3. what is your budget? prices range from $100 up to $15,000 plus (seriously top of the lines)
4. what sewing machine dealers are near her...that is important especially if you buy a fancier one...not all repair people work on all brands of machines.
5. If your budget is under a $1000, I would check out brothers, sparrow, and maybe used machines in your area at local shops as some of those might be older workhorses that have just been serviced and you could get a better machine.
6. If you budget is higher....you can get some really nice Berninas or Janomes for about 3000 Yikes...I know..this may be sticker shock...
7. At this time with the pandemic, I understand maybe not wanting to take grandma shopping....maybe you could pick out a couple of machines in your price range, share that info with her and let her pick which one she wants.
Let us know more and we maybe can recommend more specifically