I agree with Opus88. My cat had surgery recently and they told me crusty stuff on the incision is normal, but oozing or redness is not.
Is the incision oozing any thing? Or red in color? Has the crusty stuff been there since shortly after the surgery? If it's not oozing and not red it could likely be just dried blood and nothing to worry about, Do you return to the clinic to have stitches removed or are they self dissolving?
but if there is redness and oozing at all you need to take her back to the Vet clinic ASAP