The explanation could be that Gatsby, in this moment, shows himself to be similar to Tom in some ways. Jay Gatsby was supposed to be the romantic love, the understanding suitor, but he becomes insistent and uncompromising.
He becomes extreme. In doing so, he causes Daisy to recoil from him because she is frightened at the revelation of his "true character".
I completely agree with Post #3 and would add that the point in the argument that really pushes her button, so to speak, is when Gatsby demands that she tell Tom she NEVER loved him. She clearly can't do that because she did/does love him on some level. Gatsby seems to be pushing too hard for the dream of what he and Daisy had and have, and Daisy realizes that it is unrealistic.
It's because she's coming to realize that it is Tom who can give her the life she wants. Daisy doesn't really love Gatsby. She just wants some excitement. But she doesn't want the excitement if it's going to cost her her wealth and her social standing. Going with Gatsby might keep her wealthy, but she won't be as high up in society as she is now. As she realizes what she would be giving up, she slips back to Tom.