I think it's a bit petty, to be honest. Sure, baby behaviour should be stamped out, but she's only 7! What its done, is put a negative spin on an otherwise good parents evening. It's not affecting her work, or how she's progressing in school - so why make it such a big deal. You say you tell her to "ask properly" at home, so I'm sure that'll stick and she'll soon grow out of it. I certainly don't think it needs to be pointed out in a class full of other children.
I've got mine tonight (parents evening) and am expecting a mixed bag. Probably not a good time for me to mention the fact I still can't get little'uns DUMMY out of her gob, at bedtime! :-/