As said, that is another matter entirely. We don't know anything about how Faith's mental abilities affect her relationships. The most plausible answer the way I see it now is that Faith, by her pressence, seems to hit people's happy triggers slightly and it doesn't appear to be very consciously done on Faith's part. The ethics of that are up for debate and they're pretty murky waters even if we DID have something more substantial information on what is happening there, so I'll leave the mind-powers issue in the middle for now.
Now, as for Faith's partners considering themselves "cheated on". One does have to wonder exactly how much of that is on Faith, when her reputation seems to be pretty well known and she doesn't seem to ever try to hide the fact that she likes to play with a whole bunch of different girls. Knowing that starting position, if you would then get involved with Faith and feel "cheated" when you can't have her all to yourself, that's pretty much on you. It seems pretty reasonable to assume that by this point most of the girls who want to make kissy-face with Faith should know what they're getting themselves into. (And if they didn't, maybe they should've asked)
If they decide that a little heartbreak is worth the reward of some intimacy with the object of their affection, that's their choice to make.
On the same note, maybe health risks are some slight concern but that doesn't alter the fact that it's their bodies, their lives, their choices.
A lot of people do, think or believe things that I find dumb, foolish or short-sighted. But I don't judge them for it; after all, I've done, thought and believed my fair share of silly things and probably still do. And I absolutely defend their right to do, think and believe said silly things so long as they're not hurting anyone else by it.
Polyamory is Faith's personal and openly declared choice (she's all but shouting it from rooftops), so if her partners cannot accept that but get involved anyway, their hurt feelings are much more their own fault than Faith's. Personal health risks are similarly risks people decide to take for themselves. Dental dams may make sense in theory but I think a lot of people might feel they kill the romance a bit. It's a trade-off people have to evaluate for themselves.
And none of these things are anything but tangentially relevant to the issue of multiple partners and slut-shaming.
Because let's be honest here, when people call a girl a slut (additional slurs and expletives optional), they don't mean "I am concerned about you taking the necessary precautions to safeguard your physical health and that of your partners" or "Are you making sure you take the time to discuss your romantic viewpoints with your partners so everyone involved is aware of what they're getting into before you start?"
They mean something generally along the lines of "You engage in sexual behaviour with too many people for my liking. This offends my personal sensibilities of how you should act. You are a hussy/whore/other-nasty-words. Since you give away your sexuality easily it has little worth and therefore you as a person have little worth." and so on and so forth.