sounds like we all have the same story. I was living with my in-laws when I got my Doni and at first, she thought I was nutz! I was buying stuff for him left and right. I found a hitch though, I started calling him her "grand-turtle" since my husband and I don't have kids. She warmed up pretty fast after that and even took care of him if we were working long hours.
As for my mom, sis and gma that I live with now, gma thinks he is adroable and my sister is absolutly in love with Doni. She won't hold him, but she loves her "turtle-phew" As for my mom (and dad) they weren't as enthused, but they understood so for christmas they got me my whole new turtle set-up. Dad keeps teasing me.
But my mom has grown so attached to Doni that she is letting my sister keep him after my husband and I move this fall, and has mentioned the idea of keeping him herself when my sister goes to school next year
in other words - like the others have said, let your mom in on it, but don't force it. She'll either come around or not, but if you try to get her in on helping with the turtle (but do not make it like you need the help a lot) then I think it will all turn out.
I learned this from my mom though, whatever you do, do NOT let him run around in the kitchen!