Male Rana aurora will be around 3.5 inches top with visible nuptial pads. You guys are right that this individual is definitely a female. Northern red-legged frogs are powerful jumpers and are very active at night, so a larger enclosure (20 Gallon+) should be provided for one individual frog, especially for a female. Never house this frog with another individual in the same tank. Otherwise you risk disease transmission. Like all wild-caught frogs, Rana aurora can carry chytrid and these guys can do it asymptomatically, so just keep that in mind.