She'll worry about the fact that her key is missing later. Right now she's torn between being very worried over the Doctor's forgetfulness and absolute glee that the TARDIS is here. In any case the Doctor will get better now. Or he should and he'll remember where he left the key.

She laughs out loud, a real Rose laugh when the door opens. "Look at you," she teases him and steps inside the TARDIS. The floor feels familiar to her bare feet and subconsciously she holds her breath as she takes a few more steps inside. There were days she never thought she'd see the TARDIS like this again. For the moment all the pain she's gone through the last couple of days is replaced by joy.