Becoming a step mom

The father of my 3 kids got a girl pregnant while we was separated and he told me before we got back together and we are trying to fix us. He wants nothing to do with her and didn’t find out she’s pregnant tell after he left. I told him I want to be involved 100% and so does he. But she doesn’t want me involved at all. She said it’s weird I want to be included in there text messages and everything. I don’t plan on crossing any line that don’t involve the baby just want to know how the pregnancy is going. Am I in the wrong? Please help!!!