Hi! This is my first post :D
Sorry about your loss. I am sure Mr. Fishy was a beautiful fish.
To convince your mom, I would explain the joy you had with Mr.Fishy. Explain to her why you love owning fish. For me, I find watching my fish swim therapeutic. It is so calming watching the fish swim around and play with eachother.
Show her a list of the things needed to house fish, and then show her that you already have all of it.
Show her the beauty in bettas with pictures and maybe some videos from youtube. Remind her the cost of betta fish are relatively cheap, and that you will be paying for everything yourself.
As you mentioned above, she isn't denying you the fish, she just doesn't WANT you to get them. I was in a similar position with my fish. Even though my mom didn't want me to get fish, I bought two anyway. She seems to like watching them as much as I do.
Life with Lupus is still a life worth living.
Dishing out the truth one post at a time