I think if you release her now it will be very difficult to trap her again. She might take off and by the next time you see her she could already be pregnant or have another litter. A few things you could try.
Is there another vet that could spay her before the 8th?
Do you have a room you could use for mother and kittens?
Could you borrow a larger crate?
Could you wire the crate the kittens are in to the larger crate you have for the mother so all three have access to both cages?
Have you tried spoon feeding the mother? Use a long handled spoon and offer her some warmed up canned food. Sometimes if you put the food right up to their mouths they will lick it. Once they get a taste they usually eat a little.
Is there another vet that could spay her before the 8th?
Do you have a room you could use for mother and kittens?
Could you borrow a larger crate?
Could you wire the crate the kittens are in to the larger crate you have for the mother so all three have access to both cages?
Have you tried spoon feeding the mother? Use a long handled spoon and offer her some warmed up canned food. Sometimes if you put the food right up to their mouths they will lick it. Once they get a taste they usually eat a little.