I know how it feels, my Platy fish died this morning, she was 2 and a half years old I think, she lived in my tank with her son from her last batch of fry 4 months ago, it was almost like she bred on command haha, I controlled my breeding, if you want to, all you need to do, is when you think she is pregnant, scare her with the net for about 5 minutes, and she immediately aborts the pregnancy , it sounds crule, but it is called 'Population Control' P.S I am sorry for your loss, how did you put her down?