I have mice, and one of my cats gets along with them and one would eat them in a heartbeat. (I lost my first mouse that way)Marshmallow has just always been fine with them (of course they are always supervised) I would recommend having the cage in sight and supervising to see the reaction. Marshmallow has almost no reaction at all, but Pickles can't stand to not watch constantly. Then go with your gut after that.

Good luck, and have fun!