Usually it will matter more not how many partners she had in her life, but how many partners she had recently. I reckon that will more directly affect your relationship than simply the overall amount.
Like say you meet a woman/girl whatever, and she's 200 total in her whole life. Now 200 will scare a lot of guys if not most, but really if she's like 27 and started at 17 that's an average of 20 or so a year, not even two guys a month. Now if when you meet her she has a pattern that hasn't been broken yet, then that shit is a red light for you because you're just next in line so take and leave it. But if she's broken a pattern, and in this case she hadn't been with anyone for two months for example then why would it matter that she had 200 sexual partners? Maybe she was simply not able to emotionally commit to somebody before, but now she's over that stage in her life.
So yeah, I generally care more about patterns and recent history. Overall number of sexual partners might not mean anything, aside from your own insecurities. In the case of your friend given it's only 30 and she's 24, plus they have been dating for months.... I would say your friend is a bitch for wanting to break up with her.