@pdbcm As a long time owner, I'll say this is fairly common for women starting CrossFit, and I'll explain what I think is happening.
First, a chunk of it is muscle gain. If you've not lifted before an are now doing 3-4 classes a week of strength work, you're going to get a bunch of "noob gains" growth. Legs, butt, core, its all getting taxed much more than normal and I've seen the DEXAs from women before and after, this is nearly always the case. Likewise, when you gain muscle that muscle tends to retain water more, specially when you're doing heavy metcon work flushing fluids. For whatever reason, the water retention swings are a lot more pronounced in women.
Second, and maybe a bit of a dirty secret in CF, but CF generally isn't the best for staying lean. The functional reality is that high intensity cardio training creates a big appetite, and it gets really hard to control your appetite when you're doing so much, usually new, work effort. And because you just did this epic incredible workout, there's a feeling that you "earned it" so you don't police yourself as much. Its really a bit of a mind F, but if you go to any CF you'll see 5-10 folks that can do every WoD Rx, but maybe don't look like they're in great shape. This is effect is why.
And FWIW, I always try to push women to get comfortable with muscle gain and orient to "strong" not "skinny". The facts are that the quantity of leg muscle directly correlates to longevity, lifting is the #1 way to reduce the risk of osteoporosis, and lean mass actually helps you reduce bodyfat in the long term.
