I don't think Dani was being a shit friend at all, if anything the reverse. If you listen to what she was actually saying, especially the part about it being okay if Georgia didn't like Sam, she was allowed not to and should 'crack on' with one of the new boys if that's what she wanted.
I think that's why Dani got so frustrated, she and G had had that discussion, all of which we didn't see so we have no idea if Georgia said something in that which made it clear to Dani she didn't like Sam as much as she was making out, then Dani got annoyed when in front of Sam, G was singing a different tune.
Was anything Dani said wrong? No I don't think so. They can't be together in there any more, so she was right saying if that's what they really wanted they should have gone.
As I said look how frustrated we all get after an hour of just watching Georgia, imagine how it must feel living with her, trying to be supportive and realising she's not what she seems.
For what it's worth, Sam and Georgia would have been so much better if they'd said, we're not together, this is a game, let's play it for now and when we get out we'll see how it goes. Would have seemed far more genuine than them trying to convince everyone, including themselves, how much they want to be together and how hard being separated is.