Poor thing!
You did feel inside the vent for an egg?
The discharge coming from the vent makes me think she's having trouble expelling an egg - it may be a soft shelled egg which would be hard to feel.
I would give her 1/2 Tablet of Caltrate or 1 crushed TUMS. See that she's drinking well (staying hydrated). Once she's drinking, you can give a little wet feed, but food is not that important so don't worry if she won't eat just now.
Soaking is fine as long as she's not lethargic. If she is, then warming her a bit like you are doing is fine or you can provide her a heating pad on low, just make sure she can move off of it is she gets too warm.
The cockerel may have stressed her out. It's possible he may have hurt her by chasing or pinning her down but he would not have affected her vent - male chickens do not have an appendage (penis) there is no penetration during mating, instead there is a touching of the vent to transfer and accept sperm, this is called the Cloacal Kiss.
Keep us posted on how she's getting along.