I 'get' why you would feel dissapointed. You had an expectation that you were looking forward to, and now it isn't going to happen. You wouldn't be upset if staying overnight hadn't been suggested in the first place. It is understandable that you feel this way. you feel ripped off.

However, just because your feelings are understandable, I don't think it is reasonable of you to be angry at your friend because her plans no longer fit in with your wishes. Think about things the other way around and put yourself in her position. It is likely she never wanted to stay overnight, from the sounds of things money could be a big issue and on top of this all of us handle being away from our family and children differently. She shouldn't have to feel bad simply because things worked out in a way where she could still go out and enjoy you company, but still save money and be at home with her family afterwards.

Anger is usually a biproduct of another emotions, you need to deal with that other emotion to deal with the anger. Maybe just let your friend know that you're now dissapointed as you had been looking forward to staying the night, but don't push the issue or try to make her feel bad, because this really is your problem not hers.

And make a resolution to yourself to go out and enjoy your night out with your friends.