Telling my step baby

So I have a 4 year old step daughter who lives far away from us with her mom. I love her to pieces and obviously so does my hubby. Her mom is less than a fan of me although I've always been nothing but nice it doesn't matter. We are thinking of telling my step bb at 12 weeks but are concerned about her mom's reaction. We don't want her being told we love her less or anything negative but we have come to expect it at this point. She was super excited when we asked her if she wanted a sibling last time she came to stay! We planned on sending her a big sis outfit in the mail and telling her on Skype. I love her and want her to feel secure and involved! Any one else in a similar situation?