Arianny Celeste says she's super happy for Ronda Rousey -- congratulating the UFC legend on her recent engagement to Travis Browne

Remember, Ronda and Arianny clashed during Ronda's fighting days -- but now, it appears it's all water under the bridge.

In fact, the UFC's most famous Octagon girl praised Ronda for paving the way for female fighters in the UFC and called on the fighting organization to do something special for its biggest star. 

See ... what beef?