Older maids are better from my experience. They may not work faster but they are more fussy.

We had a young maid once who stole from us once or twice. But we showed fairness to her and eventually she trusted us and was more loyal to us.

I think once you show her some honest hospitality, she won't betray you. Forming a bond/attachment is key.

And about the 7kg rice a month thing, if she does a lot of housework, obviously all that energy has to come from somewhere