If you'r trainer will do a rudder roll I am sure it can be looped. The secret in looping a slow or under powerd plane is airspeed. I would not expect a .25 trainer to loop from level flight so put the plane in a shallow dive and let it buld some airspeed, then feed in up elevator, don't just slam full up, and fly it over the top, ease off some elevator and come back on the throttle so you do not buld excess airspeed on the way down. If you stall or fall off on the first try try a little more elevator, you may need full elevator to get over the top.
Good luck and happy landings.

Jerry