A soft shell or Razorback turtle would be a much better pet, they don’t get so big and are less likely to eat your fish. Me and my dad live on a lake so in the spring we used to go out and catch 2 or 3 baby red eared sliders right as they hatched and keep em until the next spring. We actually saw a couple deformed ones hatch out and kept those for a long time in a 210 until they either got too big, died of complications from the deformities, or we felt like they were okay to go back to the wild and acclimated them to the outside weather in the backyard for a couple weeks before putting them back in the lake.
We had a 90 cube which we planted with some Java fern, anubius, and moss, decorated with river stones & pebbles with a massive piece of African root we bought a floating turtle basking thing from petco and superglued some wood and fake leaves onto it so it fit better with the aquascape and put a UV heat lamp on that side. The water was warm, around 76-78 and the basking area was 88ish. We kept a couple small fish in there too like baby crappie we caught and a couple varieties of tetra and a pleco to keep things clean (now graduated to our 210 gallon cause he got big).
Just don’t put goldfish with them-the bioload is incredibly high because goldfish are nasty. Razorback and soft shells are less likely to eat any fish you try to put with them, stay smaller, and (imo) look a little better as adults. Baby red eareds are cute, but the adults not so much. We fed them floating turtle pellets, freshwater predator pellets, and the occasional bit of shrimp/scallop/mealworm/cricket because we had leftovers from our reptiles and predator fish tanks.
Good luck with the turtle! Post some pics of yalls setup and her face when she gets that turtle!
