step parent advice please!!!

So I've been a step mom for 2 years. 3 kids.. 2 boys and a girl. the girl is the youngest (6). There has been a lot of drama and harassment.. She went crazy cuz my husband moved on, got married, having a baby ect.. She has always been out to get me. She even drives past our house (no she doesn't need this road).. They have meetings at PD cuz shes crazy.. communication through email only. Well yesterday she said her 6 year old said I cut her hair. Never happened, i would not cut anyone else's kids hair its not my call. She Did get gum in it (a very small piece) it washed right out.. So of course we got accused or well I did. I'm sick of the accusations, and honestly the kid lying to her mom.. any advice? I wish we could put a retraining order against her UPDATE: thank you everyone for advice.. I love her like she's my own and I would never try to replace her mom. we do email so its all in writing and I try not to respond to the harassment unless I have to.. my husband says dont let her get to you its letting her win. just trying to vent and figure out if i can do anything legally