Etiquette?

I can see them being upset, but I'm a firm believer in not having people in a wedding because of obligation. She is young to be a bridesmaid anyways. You don't owe your dad an explanation. Not sure how helpful this is, but regardless of the bloodline, she still isn't someone you have known very long. You can still invite her to the wedding and shower if you are having one. You can find other ways to bond and get to know her.

I had a similar situation. My dad wanted me to include my younger sister in the BP, but I didn't because she and I just aren't that close. Don't feel guilty! Bridal parties are supposed to be your nearest and dearest

Make her a junior bridesmaid, a flower girl, less traditional ring bearer. If you have all those it also depends on who’s going down the isle you can pair her with a close relative if your doing it that way. I think the best bet is a junior bridesmaid and she can walk down by herself with a signing bouquet or however

What about making her an honorary bridesmaid? That way you acknowledge her without her standing up with you.

You should do what makes you happy. You only met your half sister less than two years ago, making it ten years of her life that you missed. Did your dad keep her a secret, or just keep her away from you? Either way, I’m not sure he’s in the position to judge you on what you choose. I do think it’s very sweet that you’re considering everyone’s feelings. Maybe you could include her by introducing her during the reception when they usually do the parent and bridal party introductions.

You could just give her a corsage and let her be seated as part of the processional with your parents (not sure who's walking you). But I imagine that her mother will be escorted to her seat by an usher - your sister could too. I think it would make her feel special and involved, but you don't have to include her in your bridal party.

Don't feel obligated to have her involved in any part of your wedding if you don't want to. She can come as a guest if you want to include her at all. I understand that you have the same dad, but if you just met her 1 1/2 years ago, you probably don't have that close of a relationship with her and it would probably be awkward having her hang out getting ready with you. I honestly don't understand why either her or your dad would be offended. I have 2 sisters who I've had a relationship with my whole life, they are just 15 and 11 years older than I am live far away from me so we're not that close. I didn't have them as bridesmaids, and no one cared. I could see them getting offended if you knew this girl your entire life, but it sounds like your not that close. Just tell them that you already have your BP in mind and you are keeping to to those who are closest to you. You hope that she enjoys the wedding as a guest. Your BMs, your choice. It's supposed to be the people who are closest/most special to you. If she isn't in that category, then don't make an exception just to please other people. Maybe have her do a reading or something if you want to give her some kind of role, but I wouldn't stress about it.

You can make her a junior bridesmaid or a flower girl. It's totally up to you. It's really nice of you to consider her to be part of your wedding but also keep in mind that it is your wedding so you should feel like you HAVE to do anything you don't want.