Both points are valid for narcissists. They change partners as if they were soiled undies. Not many people would be able to tell whether a girl is borderline narcissistic unless they fall into the thirst trap. My telltale signs are love bombing - if they give you so much attention and sex without boundaries (no protection/pills, BDSM/dragon drilling allowed) then you're in trouble when they start withholding all that goodies.
The best girl to be in a relationship with is one who have personal boundaries from the start and takes things slow.