How the heck can I make this better?

My husband and I are newlyweds. We have been friends for seven years, started dating, and sparks flew. Our friendship flourished into love, and we knew we were meant to be together; we eloped after dating for a year, have been married for two months, and we are very happy together.

His family and my family have been overall pretty great and accepting and welcoming. His sister has been living overseas for the past 2.5 years and wasn't around for any of our relationship. I reached out to her via email and Skype and told her I'd like to get to know her better and become friends, and she said she wanted that, too. She was moving back from Europe, passing through New York on the way back to Canada, and my husband and I made plans with her to meet up with her and her boyfriend while they were in New York and have a great time together.

It was awful. She and her boyfriend fought the whole time, and when they weren't fighting, they pretty much ignored us (e.g., made plans to go spend time with other friends, or walked way ahead of us when we were together), and were late to pretty much everything.

My husband had a talk with her about her behavior, and I had a talk with her as well, and she essentially told us two things: 1. She was going through relationship problems, and 2. She was having trouble adjusting to the changes in her brother's life. She also told my husband that it was very difficult to see him and me together so happy because she and her boyfriend were having so much trouble.

I am really offended by her behavior - my husband and I spent a lot of money and our vacation time to go and spend time with her and get to know her, and she pretty much shut us out. Or, more accurately, shut me out. She has no problem talking to my husband about what's on her mind, but told him that she felt "attacked" when I questioned her and tried to reach out. She was the one who told me that she wanted a relationship with me beyond superficial stuff before we went up to see her. Yet, her behavior was in direct contradiction to her words.

I am thinking about just writing her off, saying to heck with her. Problem is, she keeps texting my husband and wanting to talk to him alone, and he has been talking a lot on the phone and Skype with him, without me. I am planning to have a tak with him about my displeasure at that.

But basically, I think the situation is totally ludicrous and I feel very hurt by it. I do want to have a good relationship with my sister in law. In truth, it does seem like a genuinely interesting person with a good heart. I don't understand what is going on here or how to make this situation any better. Help!