As long as she's physically healthy and has no venereal diseases then her partner count isn't necessarily a detractor (to me).

What is a red flag is that this person had all these sexual encounters and never was able to form a lasting relationship with them.

Now she comes along and says, "You're Mr. Right". What exactly has changed in her psychology to form this opinion? How has she grown as a person so that this time the relationship will work out? These are questions that women never have the answers to and which often enrage them.

Maybe she can give great head and make sexy noises in bed, but everything else about her personality and history says she doesn't love anyone.

I'm not arrogant or narcissistic enough to think that somehow I'm the exception.