Betta Fish: What’s wrong with this girl?

I need some advice
I got this female betta at petsmart a couple weeks ago. I specifically got her because she looked to sad. Laying in her sad little cup, poor color, ragged fins, and overall pathetic appearance I had to ‘rescue’ her. She lives in a well planted, established tank with a couple guppies and plattys.
Here’s my question, does she have fin rot on her tail? She’s eating well and seems very happy. She ignores the other fish and they ignore her so I don’t think it’s nipping. Also, her tail has not gotten and better or worse since I got her.