The phrase "girlfriend role" refers to the behavior or characteristics that someone expects from a person who is their romantic partner or girlfriend. Full definition
Woodley (The Fault in Our Stars) does her best infusing a warm personality into what is too often the underappreciated yet overly agreeable girlfriend role. (rottentomatoes.com)
She's also perfected the hapless girlfriend role and although she doesn't have as much to do in Ted as we've seen in the past, Kunis still makes her presence known. (screenpicks.com)