Should I just let it go?
Depends how much you value your cleaner, but if she's good then she'll have no trouble replacing you. It will be much cheaper and easier for any decent cleaner to replace a client than it will be anything they break.
Granted, if this breakage took place despite you telling her never to touch the cafetierre, or to enter the room it was in, then yeah, you'd be within your rights to be very annoyed. Aside from that, you've chosen to invite someone into your home to move your stuff around, well things are going to get broken.
For what it's worth, I have only ever offered to replace anything I broke whilst cleaning, and that was a window. I accidentally bashed it whilst vacuuming, and the whole lot just smashed straight out. I told the client that I was claiming off my insurance (I wasn't, as the excess was greater than the cost of the repair) because I knew she wouldn't have wanted me to be out of pocket, but really, damaging a building is different from damaging "things" which are left lying around.
The best you will get from me in a note is a gushing apology for what's happened, and at a push a line which says "please let me know if there is anything you'd like me to do about it". However, the minute you outsource your cleaning, you have to accept the pitfalls which come with the benefits of not doing something yourself. Indeed, in one of the Kim & Aggie books, Aggie Mackenzie claimed to have a set of drinking glasses which she refused to allow anyone (friends or family) to wash, say that she washed them so that if one got broken it was "my [her] deal".