As she posed with a heart-shaped cake that read "Twenty ATE," the birthday girl radiated pure happiness ... a cow-print strapless top that exuded western charm. She completed the look with ...

"Cuter bday ever for the sweetest girl," one wrote ... a 'Poppin' Pistols Showdown' booth and a giant pink cowboy boot piñata. "Happy birthday to our sweet Chi Chi! I can't believe you are ...