Tinkerbell is not a normal summon, as she doesn't get rid of Donald and Goofy, and sticks around until the end of the fight. The description of cheer is
Increases the summons' MP gauge, giving them more time and attacks per battle. Equip to entire party to boost effect.
Tinkerbell, however, doesn't have a visible MP gauge, doesn't have attacks, and doesn't go away when out of MP. So does cheer have any effect at all on Tinkerbell? If so, what effect does it have?