4x21-4x23 Marlize DeVoe Joins

Theory
In the end of episode 20 of season 4, otherwise known as "Therefore She Is", Marlize DeVoe finally left her husband Clifford DeVoe, otherwise known as the Thinker. This has made me think about Marlize eventually joining Team Flash.

Joining Team Flash
The reason Marlize will be joining Team Flash will probably be because she'd be sick of Clifford's plan. She could also be asked for help by Team Flash. She will then most likely lend them help because she also want her husband back.

Verdict
In the end of episode 22 of season 4, otherwise known as "Think Fast", we see Iris West, go to Marlize and Clifford's first house to ask Marlize for her help. In episode 23 of season 4, otherwise known as "We are the Flash", we see that she actually accepted and helped Team Flash to defeat Clifford.