My thoughts on the weighted body rows is to calculate the percentage of body weight that you are doing when doing a body row and then make it up the leftover to closer and closer to 100% by adding weight.
I'm gonna take a guess and say body rows roughly have 70% of one's BW on them, but that just a guess from pushup BW%. It differs from person to person and I've never see any numbers with females.
When you figure out something you can 3rm that break off point, there you go. Might not be a bad idea to figure out a higher rep mark as well. Dunno.