Maybe you could show her images of well cared-for bettas and nice habitats? Make a case for getting some live plants or say you like the naturalistic look. Honestly, I’ve seen some beautiful tanks made out of large fishbowls – they sell empty bowls as large as at least 4 gallons, and you can find heaters and filters to fit them and make a satisfactory and pretty betta or shrimp habitat. Technically you can get by without a filter if you have a large heated bowl with just one betta and are diligent about water changes, especially if you have live plants (Java Fern and Java moss don’t require fancy lights). It’s probably easier to go for a cheap rectangular tank – and easier to prevent your fish from jumping out.
I’ve seen those little cyclops monster bowls, and the thing is, they also block out much of your view of your fish! What’s with the opaque sides? For a fish as lovely as a betta, you want to see as much of it as possible.
Also, maybe take the plastic bowl and put marimos in it. Use it for something, just… not a fish. They are cute, so make something cute with it.