Thanks for the help so far guys, I will try get a vent shot.
The reason I belive this female has dropped before was it was in with another female and I did see eggs with the male in two seperate occasions. I know the other one is a female as she went thin and was smallest of the group, but I'm pretty sure this one in picture also dropped as she also went thin.
But the main thing I notice was that both had these orange dots around their genital areas, which I believe means they are female in mature plecos??
Any further thoughts?