Sister in law being unreasonable help?

The last week I helped out my mother in law changed her bandages cooked meals for her moved furniture cleaned her house because I knew she had to rest and she has a habit of overdoing things because she lives such a busy lifestyle she's a lovely person and she lost her husband last year anyway the sister in law called up her mother and abused her for letting me help her for a few days. she also made her mother uninvite my partner and I to her birthday dinner and didn't end up going herself. All of this is because we won't sit down and talk to her about how we live our lives and how she thinks we should grow up. we aren't perfect but we live honestly my partner works 6 day weeks and long hours we have a 7month old we rent and are saving up for a house and we aren't married I'm going to do a course when my baby is 2 in aged care and worked prior to pregnancy in a bar this is all a big problem to her so we don't get invited to family things etc.... I've been telling my partner that we should probably get the talk over and done with but after the other day having her walk into her mothers house act like our existence offended her storming out and almost bowling me over in the process I'm finding it hard to want to mend things if she's going to be unapproachable... What would you do in this particular scenario? Should I get the "talk" out of the way? My son is missing out on his cousins and it really upsets my mother in law that we aren't on good terms too. She's been through alot