Her having more partners = more experience.
more experience = better in bed (GENERALLY SPEAKING)
better in bed = better sex with me
better sex with me = good for me
good for me = something I like
Therefore, her having more partners, generally speaking, is something I like.
As long as she doesn't have any life-threatening STDs, I say a woman can't be slutty enough! Hell, I consider myself seasoned, having slept with as many women as I have, and it has made me a far better lover than I'd have been otherwise. I want the same in a long-term partner.
It's really easy to sleep with one new person every month if you're in a college environment. If you did that for 4 years (18-22) then you'd have slept with almost 50 people! When you break it down in terms of 'rates' like that, you can see how that number by the age of 25, assuming that a woman becomes sexually active around 17-18, isn't outrageous at all.
She doesn't have a bang a schoolbus full of football players in order to sleep with 20 guys in her early 20's. In fact, confident attractive women are also playing the 3F's until they start wanting to settle down.