One way you can check for sure can be a little expensive but was worth it for me - I saw an anthropometrist.

He measured me on body fat percentage scales but since they can be out by a bit he also measured me with those tong thingies (sorry can't think of the name right now) and measured many points to get an idea of my bone structure.

I was trying to make weight at 54 kg and hold it and making myself sick. Found out my minimum healthy weight is 55 kg. I may be able to get down to 54 kg for short periods of time without adverse effect but holding it too long is dangerous for me.

He could tell me what it was safe to aim for and how to do it with minimum risk. Bone structure is unlikely to change and you can measure muscle mass on some body fat percentage scales so I don't think it's something you need to do again often.

I found when I did force the weight down to 54 kg my body fat percentage went UP!!!! I lost muscle, my body went into starvation mode and wanted to store fat. Training became harder and harder and my performance suffered.

I'll also add I think this is MORE dangerous for women. It interferes with our hormones which prevents us from absorbing calcium. Over a long period of time it can reduce bone density and increase the risk of osteoperosis. Google "female athlete triad". I suffered from this but hopefully not long enough to suffer any permanent damage.

Women have naturally higher body fat percentages than men and I know a lot of successful female athletes who don't have six packs. If you think she performs well at her current weight and hits like a train she will probably do well. From what I've seen and experienced in the womens boxing scene here the skinniest are not always the best.