Tell her casually with reference to something else that you have a camera in the room and you found out something strange. see how she reacts. Or, show your surprise that you can't find money where you had kept. Ask her does she know about it? If she gets defensive, you can take the conversation ahead. Also, with a live-in maid/nanny in the house, you should never keep any money/ valuables within her reach. Even if they come in with good intent, it doesn't take much time to get carried away given their dire circumstances.

hi anon. it's better to have an open discussion wth her and tell her to ask for something if she needs it coz it's a matter of trust. be very gentle wth her and try not to leave any valuables money out so she is not tempted. u cud give her some clothes or something she might need so she doesnt steal. pls be sure she keeps good hygiene as ur baby is small. good luck!