When she asked if Iz was preggo and Izzie said that he thinks she's 15, Mer just responded "oh" so casually, but if you remember she has NO idea Izzie has a daughter. The only one's who ever knew were George, Bailey, and Lexie, plus 2 patients (the one from season 2[pregnant teen] and the patient she was talking to when Lexie found out) but Mer doesnt know. She DID get the blood work done for Izzie for the Bone Marrow transplant, but she didnt know the specifics, she even told George that all she knows is what room she was in in the hospital "That's all I know"
Usually Grey's is REALLY, like EXEPTIONALLY good with continuity stuff like this, but i dont know what happened here, the only thing I could think of is if she looked into it all with the Bone Marrow Transplant and lied to George, not wanting to give away too much because she wasn't sure Izzie wanted him to know.
Am I wrong? Did she know? Or was she just saying "oh" to be like 'oh okay your not pregnant' but didnt really realize what she said or something??