I recently picked up a rescue similar to yours, but mine is on 10 months old and 230g.

Honestly I would try feeding her adult mice. She is plenty big enough for them. Once every 5-7 days (probably closer to 5) will help put some weight on the poor thing. With my rescue I offered it a rat pup the day I got it and it took it (probably because it hadn't eaten in 2 weeks ).

You really want to watch out for all of the things you normally would during quarantine. Anything that is outside normal ball python behavior should be investigated. I'm not an expert though, I'm currently working with my first "rescue" as well and she looks healthy, just really small.