As an older person with hand tremors these are the ones I find easiest to use. I only use herb and a small amount of that:
All are under $200:
enano or underdog log;
arizer eq (not much is easier than holding a bag and breathing from it) I use the mini whip set from arizer so filling the bag is simple. I did find it a bit complicated before I got the mini whip but now use it all the time.
milaana
I cough easily and use water for all but the eq.
I have several others mentioned here like the solo and boundless. Although good, the 3 above are easier for me to use. I may have missed whether her mental functioning is impaired. If not I wouldn't worry about her figuring things out like replacing batteries as long as tremors don't make putting the battery n difficult. I'm quite a bit older than your mom and of the 3 I mentioned only 1 uses batteries and those are easy to insert.