Who does this DH bike fit best?

The seated position doesn’t matter on a gravity bike. What matters is the stood up position. That said it seems it might fit her better but for DH bikes the sizing charts are not likely to be too far off unless you are a T-Rex or an orangutan in terms of proportions. 

An example is two hardtails my wife and I have. Seated pedaling position is similar and works well enough for both of us. But as soon as you stand up one is much longer and much better for anything steep and the other is much shorter and more nimble and better for the pump track. For someone shorter dropping the seat on the shorter bike would still make for a great bike whereas the longer bike would quickly get unwieldy. 

Kind of irrelevant posting seated pictures like this; You don’t ride a DH bike sitting on it. 

If you post standing pictures, preferably in an attacking position, it’ll be easier to tell. 

But off the cuff, the way her torso is already leaned further forward than yours while sitting, makes me think the reach might be slightly too long for her, and she’ll probably be situated too far forward over the bars when standing. That means she’ll probably have less leverage lifting the front end when needed. I wouldn’t be surprised if she felt like she was about to be thrown OTB riding that on actual DH trails.

On the other hand, your knee angle is really sharp, and with the distance between your knee and the bars, I would hazard a guess that you’ve slammed your knee on those handlebars more than once. I’d think you could actually benefit from longer reach or higher stack to help with that issue.

So, I would say it fits you better, with the caveat that you could probably look into a longer stem.