There is a level of professionalism you should have when you work at some places, but personally I think a little crass celebration should definitely be allowed.
That said, whether she knew who he was or not, her actual response wasn't necessary.
apparently Homer Hickman tried to help her get her job back, but it didn't work, but now she's an aerospace engineer at Boeing...so things are going great .
Homer didn't deny anything, he wasn't even involved in that decision. He even put in a good word for her. However she basically lied when she was asked about it and that dug her in deeper, also leaving the post up didn't help.
NASA basically wanted her to not draw controversy to the agency over social media, per their rules, and they normally have a reasonable amount of leeway. But there were a couple concerning things during the process, mistakes she made (that she has probably since grown from) that led to NASA passing on her internship.
From what I remember and what a quick search on the internet confirmed, B didn't actually deny her anything. He actually went out of his way to do as much good for her as he could. He claims to have replied "Language." because he knew other people at NASA with more say on her job would find her, which would get her into trouble (and they did find her even before his first Tweet).