this is problem from someone I'm not going to say there account name for they're safety

She/he says that when he/she says something that isn't true and she/he says even she/he didn't , her/his friend say it is true even if it's not true and the bad part is people believing in that person saying

My best advice is to ignore the person first and if the person apologizes to you then you can take it there by choosing if you still want to be friends or at least acquaintance, or stay strangers to each other

If they are bothered by you ignoring them, then explain the situation on what you feel

And if people still believe her tell it to an adult or just don't care what people are saying because it is your life, people can't judge you for it, if they are then those people are just judgemental which is not a good sign they are just bumps in the road where you take life

Yeah that is my way of doing it because I experience it myself and this is what I did
I hope it helps