Except later (esp. in her Ds9 appearances), she's perfectly capable of dialing it the fuck down. Even after getting her space-alzheimers-menopause-thing.
In the end, Lwaxana was meant to be like Mudd and Neelix - she pulled irritating shit because she was just that obnoxious and oblivious (yet also funny and likeable.) Whether that characterisation works is a matter of personal opinion.
Well, maybe it caught up with her, how much she was obnoxious to others and she made an effort to get herself under control.