perhaps tell your bf what the results you found and insist that he talk to her and tell her that he thinks this is the best printer to buy? It must be rough to have a mother like that ....i understand completely....thats personally why i take nothing from my mom...not even 5 dollars....but if you know she will insist and she wants to know what your bf thinks then just have him talk to her and say this is a good one to buy....it may not relieve the pressure about feeling insulted or having her not respect your opinion...but it will have the whole thing settled and just remember to not ask anything from her anymore...
good luck