good luck gb,
go buy your mom some flowers. I don't think we give enough flowers to our mothers and a little "bribery" won't hurt. I know I never did and because of that, I can't seem to start.
just be prepared, if she still doesn't want to return them, don't argue with her. just give her a couple more weeks. persistence and patience will pay off. meanwhile, get in her good books and be "human" to her. no one likes to hurt others, so your mom also knows how you feel.
remember, tell her (oh well, convince her) that you're responsible and that your interest in knives come from their "tool-centric" applicablity, not because you're some mall ninja or something. You also like the engineering and thought that goes behind the knife. Others will add more here.
finally, have you managed to sharpen all your mom's kitchen knives yet?