Betta Fish: Longfin in 10gal?

I have a planted 10gal that currently has a shortfin female who’s very curious and active. When I saw a 29 gallon at the thrift store I knew she would love it. So I’m setting it up for her and will hopefully add her in around new years. Which will leave me with an empty 10 gallon. I’d definitely add more resting spots if I were to add a longfin (my shortfin doesn’t use the ones she has so I only have 1 in there currently) I also just pruned the plants to grow some more for my other tank which is why they’re short rn but by January they should be back to being as tall as the tank. Don’t mind the gross filter and walls I’ve gotta clean it tomorrow.