LOL, yeah I figured I wrote wrong what I ment. I mean she already ''plays'' with memories, as in use tem freelySince when does Namine absorb others memories? She simply modifies and arranges them. She specifically affects Sora's memories because she's Sora's Nobody, in a sense.
It's true that Xemnas is likely the cause of Xion receiving Sora's memories. However, I don't see how Sora could have absorbed Riku's memories, like you suggested. Because I wasn't suggesting that.
I don't know how you made the connection between Roxas's sporadic memory and Xion receiving Riku's memory, so it can't be too much if you are making it more complicated than necessary.
If Xion transformed into Riku, then she was transformed into Roxas before (you can clearly see Roxas transforming into Xion)