Please contact the shelter. They will give you a $40 voucher to help toward the cost of the spay at any vet of your choice.
Definitely call them, bleeding can be for many reasons. If she has for sure been spayed she needs to see a vet.
If not they can point you in the direction of someone who can get a voucher for you to take her to a vet to have it done free. I hope it's that they missed that. Only because I hope nothing serious is wrong with your pup.
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