Cat owners-can a cat come into heat if neutered?

I had my female 10month old cat spayed about a month or two ago, but today when my mam was holding her there was blood on the bottom of her top, so it seemed my cat was bleeding under her tail, and she's been cleaning it a lot. I also heard her yowling a bit earlier, so it seems she's in heat but should this be happening since she's been spayed? Is there a chance the operation failed?