The question

Her visa expired a few years ago and she is scared to go back to renew her visa because they might not give to her. We plan on getting married and I am a US citizen so I know I could give her papers but how would the process be? As an 18 year old can we start the process? She has no crimminal record and she doesn’t see DACA as an option because she wants to live here legally and have a life rather than it be temporary.