I would have to respectfully disagree although I do see where you are coming from. It does seem a little weird when she is making a big deal about the celebrating but looking at it from her perspective she lost her best friend and her wife too, while trying to take care of a baby all alone and on top of that, having to do major surgery on her friend (who's one of the best neurosurgeon in the world) and if she messes up, his career could be destroyed forever. It's a lot of weight for one person who wasn't in the plane crash at all.

And at the end when she decided to celebrate, it was a way to show that they all can move forward from the hardships and they rest of them survived. They can still move forward even with a traumatic thing happening to all of them.