According to the latest edition of the Wrestling Observer Newsletter, the contract Rousey currently has in place with WWE is indeed a multi-year deal. The article mentioned that her being signed to the company was a major factor in the new television deals signed with NBCU and FOX for both Raw and Smackdown Live, respectively.

If her contract is for two years, Ronda will be a guaranteed lock for a major match at WrestleMania 34. . At that point she would have to renegotiate a new deal somewhere around WrestleMania 35.