would you say this is a good character design? what could i add?

This looks really good! You've added pretty much everything so the only thing I can think of is to add claws to the paws and to make the flap on their back into wings, but it looks good all the same!

she originally had bat wings but she lives in a swamp and can breathe underwater so i turned it into a fin

Ohh that makes sense

Btw what are their pronouns?

she/her