Hi I can give you a little insight in my situation.....
I keep a trio of Ornates together all year round, Must admit that I had them together since they were young. Both females have layed eggs for me thee past 2 years. I only seperate the female after she laid her eggs, so she can get back in shape and she wont defend her eggs towards the other ornate female, as most of the time these females will lay there eggs within weeks fro m eachother. Than after the second female laid her eggs I wait another month so both females are bakc to normal and not to defensive and I put the first female back in with the pair.
The male does have to cope with sometimes moody females during this period after egglaying, but he thats live
If it was me I would just try to introduce her just after the cooling down period (when she is old enough to be bred) and see how all 3 will get along. If everything goes fine and there is no agression other than the breeding agression of the male, I would keep them as a trio. But always have a spare cage just in case..... And make sure you spend a lot of time observing them....
Oh and dont forget to quarantaine .....
gr. Kamiel
