Our dog was spayed, but she bled from her vagina a bit ago and started again, the second time this year. help?

When she first started, a stray dog of her same species started appearing around our house. It left after she stopped. Now today she has started again and the same dog showed up with a friend when we let her out, so we quickly put her back in. She has been constantly sitting by the door wanting to go out. She has made no change emotionally. Is it possible the spay she got failed? She is 8 years old and was spayed asap and we got her as a puppy. Why is this happening? Its impossible for sexual organs to grow back, she isn't a magic dog. What is this? She is showing all the symptoms of being on heat. What is this? When it last happened I think my parents took her to the vet, but I forgot what happened. Pretty sure they said nothing was wrong and we paid 350 for nothing.