Why wont my chihuahua wont eat her food?

she is alittle over a year old and weve been giving her hard food(purina) since she was a puppy but she seemed lke she didnt like it anymore so we switched to soft food(the one with the white dog on it) and she loved it then got tired of it, then switched back to hard(purina) and now she barely eats at all. shes always asking for treats instead. can you please give me some names of food your dogs really like? please and thankyou(: