I think somebody mentioned this & I did not read the 2nd 2 pages: the shop can say "It is our shop that was visited last. We can B liable for anything wrong. We did not like xxx & changed it for safety."
Use just one (may B here fav right now?) shop. Go to that shop and say "I will B watching ur service for my (grandmother, mother, neighbor, friend). Treat her no different than you would a thirty some gentleman w/some car knowledge. No more up-sells or I'll be in to ask for a difference."
Otherwise
2) have her go toa shop you currently use / respect / have a relationship with.
3) Accompany her
4) Talk to her abt ur care & concern abt her, not "U did it wrong".
One or all 4 ?
Good luck, thank you for your human neighborliness. We have a 7 house/family deal like this (in'n out of each other's homes, care for like family due to the corps spreading us all over'n w/o our own families where we all grew up). Family of choice...