The Republic of Ireland international defender joins the Reds after five years at Manchester City, where she helped the club to a domestic treble, along with several other trophies.
The 27-year-old full-back also gained Champions League experience, though her finest moment arguably came in the 2017 FA Cup final when she assisted two goals in front of a 40,000 crowd at Wembley.
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Campbell joined City from the American college system and her time at the Florida State Seminoles brought one national title and one runners-up spot.