Is breaking off communication with a harmful female relative after she has left the home considered a severing of the ties of kinship, incurring sin, especially given that the relationship between you had previously been marred by harm from both sides?

If she is one of the close relatives with whom maintaining ties is obligatory, then you must maintain ties with her through calls, messages, or gifts, and boycotting her is not permissible. Allah the Almighty says: (Then, is it to be expected of you, if ye were put in authority, that ye will do mischief in the land, and break your ties of kith and kin?). Boycotting is permissible to avert harm. However, if she is one of the distant relatives, there is no sin upon you in boycotting her, but it is better to maintain ties with her and endure her harm patiently.