Okay, I read through this twice to make sure I had the story correct. So, she is the one making the accusation that he does not like her, but loves her. I'm going to try to be objective here, because I've been in similar disagreements. I have gone so far as to at least admit, in times of extreme duress, "I love you, but I don't particularly like you right now." He hasn't said anything of the sort. She is making the assumptions based on his nastiness. I understand this, and it's completely natural when long-time couples get heated about things. It sounds like he is passive-aggressive, and maybe feels a bit emasculated during familial arguments. She probably feels that she's doing everything and getting very little in return, which makes her frustrated, and if she's a firecracker, she probably just gets right into it and lays into him.
One does not have to be 'childish' to have control issues. My advice would be for her to rethink her communication strategy. Rather than make accusations, take a few deep breaths and have a discussion instead. Obviously, I don't know your friend, but I think that might help. Also, he needs to start saying what he REALLY feels, rather than relate to petty insults. Given what you say is his nature, he probably won't until she changes her method of communicating. I would guess that telling her that will probably make her go ballistic, but trust me, it works.

It's all about compromise. She may also want to think about why she's staying, if it's such a misery. If she discovers that it is indeed out of love, the answers to resolving the communication problems on both sides may become more clear.