They are beautiful, cheaper to care for than a cat or dog, they are something to learn from and educational, they dont smell, soil carpets, you dont have to takem for walks, bath them, they arent noisy, they rarely bite, arent dangerous, and are easy to care for, and live a long time. Good luck Cookies.
I used to have to same problem cookies. What I did was taking up the discussion again and again. I had lots of literature about that topic and showed it to my mum. Guess I was getting on her nerves . But I was successful!!! Sometimes she said: Ok but please buy a tiny little thing! That seemed to be a fair compromiss to me. So I bought my first T. It was a P. formosa about 1 or 1,5 cm in length. My mum was totally enthusiastic from the moment on she saw the beauty of that little T. . At the moment I keep 5 T. and now she uses to water the tanks when I'm not at home . In the next weeks I will buy 5 more T. and that's ok for her. But I think I must say that is most likely not the normal case. Just keep showing her pictures and tell her about the beauty. And as savior said keep counting the positve aspects comparing to other pets.
Just don't give up! Guess you will have her sometime.