First time owner

First time beta fish owner. I had a little 3 gallon tank, but I am going to get her a larger one soon. I took her because she was at the bottom of the cup clearly and distressed, and once I got her into the tank and saw her swimming, I noticed this yellow string hanging from her belly. I did treat the water. I’ve tested the water and it comes back. Perfect. I do also have bettafix- have not used. I purchased some bug bites beta formula, but it did not float at all. It just sinks straight to the bottom. I did give her a mealworm treat. Other than that. I haven’t honestly watched her eat any of the pellets. So I’m not putting any more in there right now because I don’t know what’s going on with her. She is swimming a lot. She comes up and takes a breath. She genuinely doesn’t seem distressed unless swimming a lot is a sign of distress. I just don’t know what this is hanging from her bellyif anybody has any advice for a first time bet if anybody has any advice for a first time betta owner please chime in! Other than size of tank, I do know she needs a bigger space, and live plants etc. I am specifically wondering about this belly string and her not really eating . It can be seen better in a video so I am trying to figure out how to post a video of her. hey can be seen better in a video so I am trying to figure out how to post a video of her.

First time beta fish owner. I had a little 3 gallon tank, but I am going to get her a larger one soon. I took her because she was at the bottom of the cup clearly and distressed, and once I got her into the tank and saw her swimming, I noticed this yellow string hanging from her belly. I did treat the water. I’ve tested the water and it comes back. Perfect. I do also have bettafix- have not used. I purchased some bug bites beta formula, but it did not float at all. It just sinks straight to the bottom. I did give her a mealworm treat. Other than that. I haven’t honestly watched her eat any of the pellets. So I’m not putting any more in there right now because I don’t know what’s going on with her. She is swimming a lot. She comes up and takes a breath. She genuinely doesn’t seem distressed unless swimming a lot is a sign of distress. I just don’t know what this is hanging from her bellyif anybody has any advice for a first time bet if anybody has any advice for a first time betta owner please chime in! Other than size of tank, I do know she needs a bigger space, and live plants etc. I am specifically wondering about this belly string and her not really eating . It can be seen better in a video so I am trying to figure out how to post a video of her. hey can be seen better in a video so I am trying to figure out how to post a video of her.