Sister declined bridesmaids invite

This is why I think making a big deal out of asking people to be in the bridal party is ridiculous. It puts people on the spot and may cause an embarrassing situation if they don't want to, for whatever reason. People take the wedding thing far too personally. Who cares who gets married first and some people feel they can be a better support system to you as a guest and then as a BM. She's your sister, just ask why.

My sister and I are not in each other's weddings. She didn't put me in hers so she is not in mine. We have never been really close but it completely devastated me that she wouldn't put me in her wedding. It sucks.

You should talk to her privately. She probably has a valid reason that she will share in private. It could be for the best. One of my sister's agreed to be one of my BM's and she has been a bit deflating. She is up and down with depression and I have basically stopped talking about the wedding all together with her. She has also decided she cannot stop by my wedding shower because it was scheduled on my nephew's birthday. Not even stop by for 15 minutes. I've sacrafised tons to be there for her and her boys. Anyway, if your sister's heart isn't in it and she cannot support you as a BM, it's good that she let's you know now instead of disappointing you down the line when you need her. Good luck!

Talk to her about it. Like others have said, it may have been too much pressure in front of everyone, or it could be because she wants to be you MOH. We can't put ourselves in your sister's shoes, so you'll get further by talking with her.