If she's still very young (and I guess she is if only just mobile), then no one is going to expect her to have impeccable (or any) manners. However, they will expect you to be showing her what is polite and what is not, however much is or isn't registering with her at the moment. And where she's doing something that upsets another child, they will expect you to intervene sharpish.
So if she grabs a toy another child is playing with, then saying 'its not nice, wait your turn' or whatever, and handing the toy back, will be much appreciated by the other child's mother. Followed by quick distraction on your part to try and head off the resulting tantrum. If you're lucky, the other mum will say 'its nice to share' to their child and let the toy go (a bit like 'after you' 'no, after you' 'no no, after you...').
Until she's much older, you're basically the interface between her and the world outside, so as long as you are behaving in a polite and considerate way, I wouldn't worry about there being any 'hidden' etiquette, or about your baby/toddler behaving like all babies/toddlers do.