She already told you what it was. "My friends told me I should start dating a nice guy like you", meaning she isn't dating those 'nice guys' of her own volition right now... meaning she isn't inherently attracted to 'that type'... meaning if she dates you, she will be 'cool' with you and will probably end up using you as a provider as you later discover she's going right back to those guys she shouldn't date behind your back. Solution? Personally, don't put too much stock in her and find a woman that likes 'your type' naturally as opposed to dealing with a woman that is 'settling' for you, and dealing with you because her true attraction type isn't cutting it.
Attractive women get tons of attention, meaning they can date who they want, when they want more times than not, unless it's some top echelon baller type. In other words, if she wanted to kick it with 'the nice guy', that's exactly where she'd be at... probably married to a nice guy, raising her family. Her friends had to tell her to stop dealing with her natural type, meaning that she's exactly where she wants to be, and if she got with a nice guy, at most he'd be a rest haven.