Seeing as though the whole point of educational programming is to teach kids, and technically you could call any kind of teaching brainwashing, to some degree, yes. Elmo is used to brainwash kids. Though I wouldn't call Elmo as much a tool of the man as some other things, since PBS usually has its shit together, at least moreso than 95% of cable or commercial network programming.
That said, I can only speak to my own feelings about Elmo, which are that he's creepy as fuck. I don't know if he's literally, actively evil.
But everyone like candy (except for communists), so you should probably just buy her some anyway.