In the novel she does enter the shop at some point, although I can't remember if she was working. Also, in the scene when Qui-Gon tells Shmi and Anakin that Anakin is free she is sitting at her work desk with lots of little pieces of machinery and parts. I think she might make certain gadgets and machines for Watto.
Yes, DD, I remember she was sitting at what looked like some kind of work table with all kinds of small machinery. Still, being slaves, their place certainly wasn't a dungeon. According to the book, there was a main room/kitchen area, Anakins room and Shmi's room. Not bad for slaves on a planet on the outer rim.
Yes exactly as it says in the Insider's Guide. She was indeed a house servent and now cleans machine devices. Also I think I heard that when in Watto's Shop she cleans racks and things like that, just as Anakin does.
I don't think that either of them have a particular job or routine. I think it just depends on what Watto tells them to do. If his junkyard needs to be sorted out he might tell Shmi to do it and if his shop is dirty he might ask Anakin to clean the place up. It all just depends on what Watto needs rather than a single type of job for each slave.