To begin with, we don't know that she has told this guy that she loves him and wants to marry him, and no, I don't consider it a rebound. Maybe she just felt "something different with him, some real adult chemistry.
I dated a guy for 4 years, I loved him dearly, he was my best friend. When I met my husband, it was different. The chemistry was different. I knew he was the one for me.
The guy I was with before was my best friend, we grew up together, but he was not the man for me. I did not love him as a man, but as my dear friend. There is a difference.
It was not love at first sight, but we both knew there was something there, and we went with it.
4 years later we were married and have been married 33 years