Betta Fish: I found this betta like this :(

So, to start, I got her at a petco a week ago. I didn’t originally go in to buy a betta (i know irresponsible of me) But i saw her in a tank with fish much larger than her with nubs for fins and decided to get her. The people at petco had told me she came to them like that but with how ragged her fins were i didn’t really trust it.

I was wondering if anyone had any tips for getting her fins back to a healthy point, she’s started getting some blue flecks on her fins which i hope is good, but besides that I’ve only been putting in medicine from walmart into the water for her. Are there better medicines to use? Also, is she a healthy weight?

(also side note, she is easily the friendliest betta i’ve ever seen. i have 4 molly fry in there and she hasn’t bothered them once!)