^^ that. If it's been a bit engorged when she's tried to feed it could be that she then hasn't had a very good latch due to the engorgement. Sometimes just taking a bit of the hardness away so they can get on helps.
Warm compresses before, as you're doing, with some massage to get things moving will help. If it's sore, some cold compresses afterwards will help too.
Have you tried feeding in a different position on that side? Rugby ball, perhaps, so it's a similar position as on the left which she's emptying better.