My 4 year old step daughter is a brat!?

My husband and i each have a daughter from past relationships. mine is 7 and his is 4 almost 5. Her mother lets her do what she wants with no discipline whatsoever because she dont want to upset her but she calls sometimes crying that she cant handle her. so my husband says to discipline her but she says she cant cuz shes a "baby". We have rules at our house so when she comes on the weekend she tries to do what she does at her moms but when she gets punished (time out or no tv) she cries for her mom. Her favorite things to say are "my mom dont make me or my mom says i dont have to". worst is mealtime, we make our girls eat all their food which isnt much but shes picky and puts up a fight and when we make her she cries for her mom. her mother even gives her a choice if she wants to come to our house or not.Shes 4 years old, she shouldnt have that choice! my husbands really upset because shes getting to the point where she doest want to come to our house with rules.