Language / Advice on Polish word - possibly colloquial? [4]

Hiya - I don't speak polish so have difficulty with the phonetics, I keep coming across a word that I am desperate to know the meaning of - it is spoken by my neighbours to their dog (her name is Nell) repeatedly and I'm sure it means something like 'bad dog' or 'naughty' - my transcription of it (without having IPA fonts on my computer!) is something like /nieWOLno/ (in english would be pronounced something like 'neeVOLLno!').

Is it some kind of affectionate form of 'Nell'? Like I call my dog 'doggles'?

Cheers!

J