What should i do i my ex won't let me see our daughter?

my ex and i went through a seperation. we have a daughter out of wed lock. i know that state law with missouri is she has full custody of the child. she won't let me have my daughter if my new girl friend moves in with me. so what i am after is if i get a plan parenting custody with ex finalized in court, could she still keep me from our daughter?