You want to have them meet on neutral ground a place, room, floor that sofie hasn't been. Then you'll need to have the cage they will be in totally clean, meaning trying to not have Sofies smell on anything and also rearrange it as much as possible so it seems new to both of them.
During the first 15 to 30 min you should be able to tell if they accept each other. Give them ONE plate of veggies to share and some hay during the introduction. Them sharing food is a good sign.
You will probably see butt sniffing, sniffing under the chin, mounting, rumble strutting, it's hard to tell when they move to the dominance faze ( for me anyway) and some chasing maybe. So long as no one draws blood or seems overly agitated things should be fine. Very agitated is teeth chattering, raising up on back legs, biting.
One of them might squeal as if hurt but this is most likely just her submitting and saying leave me alone. Don't separate them unless you see blood or them rolled into one big ball of fur and have an oven mitt (to grab with) and or large towel and throw it over them ( it will distract them) DO NOT STICK YOUR HAND IN THERE UNPROTECTED!
Sows are much easier to introduce than boars. Just make sure that the cage is large enough for two sows to live in at least 7.5 sq feet I believe, but bigger is always better. You will also need to have two of everything, beds, bowls hides and water bottles so that they don't have much to fight about or get possessive over.
I'm sure someone else could give you a better answer but I think they're all asleep across the pond lol. I didn't want you stressing out all night.
Not too long ago I introduced a third sow to my two and things went very well, but I was a nervous wreck.
I think there are some stickes above on what to look for and how to do it.
Hope I helped,
Angela
