Rat hair loss

I’ve had this rat (Barriss) for about 4 months now, when I first got her she had a small bald patch however the previous owner said it was just over grooming. She came with another cage mate (inigo) who has unfortunately passed about 2 weeks ago. I don’t think inigo groomed her and now that she’s gone I know that for sure.

I currently have 2 other rats (Sevs & jinx) who she socialized great with. I always catch them in a rat cuddle pile. I’ll occasionally see Sevs or jinx grooming her but it’s never too often. I’ll occasionally see Barriss grooming herself but it’s never consistently.

Barriss has lost tons of hair in the last week. She’s always been a little bald on her underside but now it’s completely hairless! She shows no signs of infected skin and my other rats are not experiencing the same hair loss.

I’m unsure if it has to do with her diet, when I first got her she was on a rotation of oxbow essentials (adult) and full cheeks rat and mouse pellet diet. I don’t use full cheeks with my other girls so I winged her off and she seemed to be doing fine.

It feels like she’s losing more and more hair daily, any advice or help would be wonderful and GREATLY appreciated.

Additional info: -the first pic is when I first got her, the other two are from today. -Barriss is a year and 5 months -I don’t know where the previous owner bought her -Sevs and jinx are the same age as Barriss -Barriss is a standard and the other two are dwarfed.