More than likely it is rude assuming as you stated that she meant to do it and seeing she didn't apologize --- rudeness comes from when you are impacting other people. Most people would not appreciate the smell, noise and find it disgusting. And the idea is in a library you are supposed to be quiet so just the loud noise is rude and probably can be heard throughout the library so yeah I vote rude.
Ideally in such an environment you excuse yourself and go to bathroom. Sometimes though it just sneaks up upon you and you don't mean it then a simple excuse me is sufficient.
signed the rudeness police