Not sure how young a young adult daughter is but if she's not yet in university, say the usual mum stuff- "we support family- we don't make people feel bad for their accomplishments" etc.

If she's in university, and especially out of the home, address her as you would any adult guest, that she was very rude and those kind of comments are not welcome. Keep it short and simple but nip it in the bud.

Otherwise your post reads as 'how do I stop one of my kids from being mean to the other'... is this a serious question??

Please say something (firm is fine) to stop this behavior, protect your youngest, and insist upon civility. It may not work. Keep doing it anyway.

I was the snarky older sib. I deeply regret how cruel I was to my sister when we were kids. We are in our 30s now and just recently starting to relate better. There were jealousy and favoritism issues, sure, but mostly I had learned to be sarcastic and cutting as a way of communicating - yep, from my parents - and just thought it was the way we talked. It wasn't hard to stop but somebody had to tell me it was rude and alienating.

Tell her that nastiness will not be tolerated.

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I wouldn't say anything about her behavior. I would talk to her about what she's going through, express empathy, maybe do something special with her. Emphasize that your proud of her regardless of her job search. Help her feel better, she'll treat others better. It's hard to celebrate someone else's success when you are going through a rough patch. Yes, it's petty, but even adults have a hard time. Praise any positive interactions you see between the two!

She is not a four year old. She is a young adult.

You tell her to knock it off, she is being immature and rude and not acting like an adult, and that as a memeber of this family we support each other and celebrate and acknowledge each other's achievements. You tell her she is not a 13 yeat old going through middle school and puberty so she needs to quit acting like one, and if she must be rude she needs to not say anything at all.

+100

This

+1. OP, don't worry so much about how your older DD will feel; worrying if she will get her back up, etc. Because she may have learned that getting her back up will prevent you from challenging her.
I don't like this idea that it's hard to feel good for someone else if your life is not going well. I don't believe that is true; I think that some people see a zeor-sum situation when they should not. Older DD should not be competing or comparing with younger sibling; their lives are different. She should not have the luxury of feeling so sorry for herself that she feels entitled to take it out on younger sibling. I love the "straighten up/fly right" advice, the advice above, and some other comments--basically the comments that tell you to straighten her out and defend the sibling--model your matriarch role, remind of the rules and the appropriate mindset. Think mama cougar--nip your misbehaving cub and nudge her in line. She'll be mad at you, but down deep, she wants it....she is looking for the boundary, as all kids are when with their parents.

Anonymous wrote:Just say factually and objectively. "You're being a bitch. Quit it."

I agree with this.