That whole 'hello sweetie' thing got me confused.
Although she did say that she called the Doctor and got the wrong version. Perhaps she said that because she knew he was the Doctor. The Doctor might have told her about the regeneration thing, which would explain why she wonder about his change in appearance.
She also said that this (him being Doctor #10) was the youngest she'd ever seen him, and she seemed surprised by that, so I'm guessing she never saw him like that before.
At first I thought she met him as Ten, but then when The End of Time aired and she wasn't involved at all, I either thought that the writers messed up or that she thought he was a future regeneration.
Very strange, but I still find the Doctor's future being River Song's past one of the coolest things in the show.
"I'm sort of like a child genius without being a child or a genius."~Tim Rice-Oxley