JoshWright: As a waiter who works in a very busy restaurant/function centre I see where she's coming from. Everyone has their moments like forgetting how many people are at a table/if more are coming etc.. The highchair thing is a bit weird but honestly in a hospitality work environment you need to clarify everything/ask excessive questions.

Had a lady yesterday order an English Breakfast tea which I took to her table 5mins later only for her to ask why I served it with standard milk rather than Trim. Did she ask specifically for Trim? No, she assumed I would just somehow know she preferred trim. 

Bottom line is both waiters and customers can be idiots and if a simple question can clear something up then don't be a dick about it. To be quite honest I'm offended you assumed she was under the influence, I'd like to see you try working hospitality! It's tough.