This is a long one...

I need another prospective. So my step daughter's play is this weekend. She's 9. We are having a family day out sat, the one day she doesn't have her play and are going to tell her she's going to be a big sister. My hubs ex just told him she wants us to wait bc this weekend needs to be about all about dd. We've got a shirt made that says promoted to big sister, we were going to tell her and then go on and play more games and have a good day. We wanted to make our day about dd and having a good time with the 3 of us (which my retail work schedule doesn't allow often)and then tell her. It's not like were going to dwell on it and shove it down her throat. I'm just pissed that she's trying to control everything again. I literally don't want to do it now at all ever. She continually sucks the life out of what we have going on when it deals with Dr. She majorly impacted our trip to Disney where 3rd didn't want to go do anything. Am I wrong to feel this way? I get where she's coming from and that she's been an only child for 9 years but we've literally slipped up in front of dd and thankfully she didn't catch on. She thinks it's going to greatly upset step daughter. I don't know which way it will go but she was so insistent on that that it makes me wonder what she's been saying to dd. I love this little girl like shes my own and im concerned how she's going to take it and we're prepared to deal with it however she reacts. Sorry this is so long. I just need to get it out to make sure I'm not off the deep end on this. Are we wrong to tell her bc she's in a play this weekend?