Need help with introduction

I have a sow and a boar that have been together pretty much their whole lives and I trying to introduce another smaller (100 pounds around) sow but the boar is no trouble but my very territorial sow is not giving up with the constant chasing and trying to nip at her side one time she slipped and the sow threw her into a big spruce tree help please urgent

It is a good idea to introduce them across a fence line and then to a new area with lots of food provided while the old areas are still available for retreat. It is normal for pigs to be territorial at the introduction of a new pig and fight to establish who's boss. The worst case is with evenly matched animals. With a large difference it generally works out better as the smaller one will recognize the larger as boss. It also helps to introduce many at once to reduce specific aggression. If they can not get along at all then consider separation or who to cull.