Whenever I add a female, I rearrange lots of the fake plants and ornaments (re-establish territory), and like you said float them. Sometimes though you can always get an aggressive girl that needs to be by herself. I suggest just keeping an eye on them, making sure eventually she does leave them alone. Sometimes it takes a week or so for everyone to get used to each other.
Breed for the breed, not for the money; the words any REAL breeder would understand.
You must know nothing in order to know all, for all is nothing and nothing is for all.