Is 'Being in Love' sometimes a mental illness?

The reason I ask is because today I heard, on the radio, an interview with a young woman (32yrs+2kids) who has been a victim of domestic abuse. She has just published a book about her ordeal.
Her abuser had beat her severly and gouged her eyes out leaving her totally blind. Horrific.
The thing is, when asked by the interviewer, If she loved him?, she replied that she still did for some months after the incident. This, I must admit, shocked and rocked me.
So, what is going on with such women?
Can you shed any light on this kind of thing?