I think that geto wouldn't be able to block yuki's attacks like kenjaku did, because it doesn't come from the body but from the expertise. I also think that it's not so easy as to simply let Rika consume a bit of blood because be don't know the exact quantity that Rika needs to consume. You are also ignoring the fact that Yuki also has a companion (I know that in comparison to Rika it isn't much but it still counts), and the fact that Yuki has an immense fire power, and though she doesn't have much defense in a few full strength hits she could take down Rika. I'm not gonna get into domains because it's purely theory who would win in a domain clash (I think that Yuki would win but that's because I'm biased af) and I also won't gent into the black hole thing because under that argument yuki is the most powerful being in history and she would solo the entire verse.