I work as a gardener, and while I never expect anything, it's always appreciated when I get a bonus as I know it means people appreciate what I do.
I'd give cash if you can - maybe with a note telling her to spend it on something special. Unless you know her well, gifts are trickier - many of the ones I've been given have ended up being passed on as they're not really me. And while I appreciate the thought, I'm always a bit sad that I couldn't have had the (much needed) cash instead!
Of course, my work being seasonal, this is the start of a lower income for me, so money is more of an issue. But I have friends who are cleaners whose work drops off over Christmas as many people are home from work and happy to do their own (plus with Covid, clients who are working from home and doing their own cleaning because of that) So I'm sure the money would be appreciated.