What can you do if someone is harrassing you in your own home?

A friend of mine is living with her ex, and both of their names are on the lease. But my friend is paying all the bills and getting harassed by her ex. She fighting with her, pestering her constantly and it's starting to effect her because she getting to work late flustered because she's always around. I really don't know what to tell her, so i needed some advice on what she should do.