Mending broken relationships with stepkids

My stepdaughter isn’t fond of me even though we had a great relationship when her father and I started dating. She’s in her late teens and away at school most of the time. We told the kids this weekend that we are expecting, his son was fine but his daughter thinks this is all my fault and I’m more awful than I was before. I’ve tried so hard to mend the relationship but she says there is nothing to mend. Does anyone have any ideas as to how to help her adjust to having another sibling? Or is it time to just leave her alone and let her live her own life? I don’t want how she feels to drive a wedge between his son and I or even my so and I.