Hi
Breaking up is very hard to anyone in love, and even though we know that the person is not right, the loneliness takes a lot of will power.
And the mind plays us tricks like just recalling all the good moments.
So, for anyone there is a temptation of going back to the relationship.
It requires tallking about both sides of the relationship: the good moments and the bad ones to gain the strength to make the final decision of not going back.
It also requires support from friends and family. So listen to your daughter and ask her about the good things and later about the abuse, so she can realize what is the reality of hte realionship. Aks her about her feelings and emotions, sharing them can be helpful.