Is it permissible to take food or money from the husband's mother without her knowledge, knowing that she allows and does not object to that?

There is no harm in eating from the food of the husband's family home or taking from the mother-in-law's money when in need, without repayment, as long as their consent is known or explicitly stated. Allah (the Most High) says: {There is no blame upon the blind, nor is there any blame upon the lame, nor is there any blame upon the sick, nor upon yourselves, if you eat from your houses, or from the houses of your fathers, or from the houses of your mothers, or from the houses of your brothers, or from the houses of your sisters, or from the houses of your paternal uncles, or from the houses of your paternal aunts, or from the houses of your maternal uncles, or from the houses of your maternal aunts, or from [houses] whereof you hold the keys, or [from the house] of your friend. There is no blame upon you whether you eat together or separately} [An-Nur:61]. Customary permission is equivalent to actual permission.