How do you interpret something like this?

I'd let it go.

Honestly, SIL was a pain during wedding planning, and still owes me an apology.

But I'm deliberately - and rather pointedly - doing my best to take the high road. The pure one to whom all things are pure. (Honestly, MIL was fed up with her own kid.) If you stay cool, calm, and so polite you'd personally drive world peace.... you look good. And her own behavior will tell.

I tend to just ignore side-comments like this. My partner and I come from very different families. They're very, very passive aggressive about things over long periods of time involving the entire family to say "person A told person B who told person C that you were mean over the vacuum cleaner" or something. I'm not used to that kind of thing - my family is very pointedly aggressive and talk things out and move on to being happy again in like 15 min tops. It sounds like you have a passive aggressive issue with your SIL here, too. I ignore the comments simply because any time I respond to them, I seem aggressive and I've learned it isn't worth it. If it's a real problem, they'll say it to my face and we'll talk about it like adults, but the passive aggressive thing is childish and unnecessary. I'd suggest you do the same thing - just ignore it and if it's a big enough issue for them to really complain about, they'll find the guts to actually talk to you about it.

I'm sorry you're going through this. I have a similar relationship with my sister-in-law. Not my husband's sisters (we get along great), but my brother's wife. In my personal opinion, I wouldn't think too much into it. Don't let her see that it's bothering you if it is. I know it's frustrating and it's hard not to say something about it, but try to keep your cool. I'm not going to get into the situation with my brother's wife and I because that would take you all day to read, but once I stopped showing emotion and stopped showing how what she was saying was hurtful and bothering me, I felt so much better and I was finally able to let it go. I still have a great relationship with my brother, as I always did, but I don't communicate with his wife unless I have to. I've tried numerous times to talk to her and fix whatever the issue is, but it seems like she doesn't care enough to talk to me about it so that's where I left it. The crazy thing is, her and I had an amazing relationship up until about 4 months before their wedding. From that point on, nothing I did or said to her was right. But anyway, like I said, I've been able to let it go. It takes too much energy to be angry at someone and it's not worth your mental health to try and please them.

I agree with pps that her message only has an underlying message if you interpret one and react to it. If she really is trying to create drama, that 100% depends on YOU reacting to it. If you ignore what you perceive as hidden messages, it will likely become pointless for her to make them (if she is in fact trying to bait you). From an outsider's perspective, "yeah, I never met her cousins" could just be a statement of fact, not an attempt to call you out for not making sure to introduce her. If I'm following your post, I think you're also indicating that she didn't know you were listening to the conversation. If that's true, why would she be trying to start something by saying something she doesn't know you're listening to? You say she sounds "entitled," but then your suggested/hypothetical response back to her could be interpreted as really snotty (e.g., "...I'm too busy getting married"...). It takes two to create and keep drama going. If you don't want drama, don't engage or look for it. Try to at least act like you take what she says at face value and don't react -- life is too short. Being happy is the best response. Good luck!