Need your help

I am not a United States Citizen (yet) but I want to know if my friend was in this country for the past 6 months and went over her stay what can I do to keep her in this country without having to go back to her country?

Please help me out.

I am not a United States Citizen (yet) but I want to know if my friend was in this country for the past 6 months and went over her stay what can I do to keep her in this country without having to go back to her country?

Please help me out.

Assuming you are an LPR, you cannot do anything. Marrying her won't help because she cannot adjust status.
There is no fiancee visa I believe for green card holders either.

so even if i become a citizen i can't do anything to help her out and she will have to return to her country. so there's nothing that she could do either?

If you become a citizen, and marry your girlfriend, you can file the petition and most likely she can adjust status (unless there are some other undisclosed problems).
The reason why doing this as an LPR won't work is that the petition you file (the same I 130) won't be what is called "current" - that is, no visa is available for spouses of LPR's because there are only a limited number available each year and there are far more people who are waiting for them - hence the approximate 5 yr backlog.
But there is no numerical limit on petitions & visas for spouses of American citizens.