flase maps fighting?

[kiki-marie]

Hi all, I'm new to the forum and have been trying to search for some answers to my questions, but had no luck yet.

I have three female false map turtles (I'm pretty sure they are all females) recently the bigger of the three has started fanning and snapping the smallest, but hasn't cause it any injury so far. They're a year and a half old, and have all been together since a few weeks old and have never had any problems before.

Is there anything I can do to stop them fighting (putting them in seperate tanks isn't an option as I only have the one) or will I have to find a new home for the bigger one? I've read that RES turtles can fight really aggressively. And even kill each other, but I'm not sure about false maps.