Here's a link to help understand the head weave.

http://www.quite.co.uk/rats/#Head-weaving

As long as she's just doing that weaving thing, it's no biggie. If it's a constant head tilt, it can be a health issue. Here's an excerpt from the link (you might want to head up on wry neck and head tilt to make sure she's not showing these things)....

Head-weaving is often seen in rats with pink or red eyes. The rat will usually stand still and weave its head from side to side for a while. This is perfectly normal; all rats are short-sighted (although they can sense movement from some distance, they can only focus for a few feet), but any animal with pink or red eyes has worse eyesight than those with dark eyes. Moving the head from side to side helps the rat to judge distances and the depth of objects by making them appear to move. This should not be considered a fault or problem - rats sense smells, sounds and movement (by feeling vibrations on the floor) much more acutely than humans, and can cope perfectly well with limited eyesight. Note that there is a different, unrelated condition called head tilt or wry-neck, where the rat holds its head on one side permanently. This can be caused by a inner-ear infection, or a brain tumour; it needs urgent veterinary attention.

I've seen it occasionally with some of my red/pink eyed rats though not often, just here or there with a few of them.

Pregnant rats generally develop a distinct pear shape about a week or so before giving birth and will nest build around 24-48 hours before delivery. If you believe her to be pregnant you can leave her in with the other two females, they won't bother her or you can seperate her out, which is a bit easier on her to not have to jostle for food or water and get a bit more quiet rest before the pinks arrive.

As far as jumping on each other, that's just play and some establishment of who is boss rat in the group. Rats are very social and like most social animals use play as a way to sort themselves out. Rats will often stand upright and box, wrestle and so forth. One of our biggest males has always settled down the irritating younger males by simply stomping over and sitting on them/flopping on top of them LOL.