My puppy has blood in her poo she is 11weeks old happy lively dog

If your puppy has blood in her stool, then she probably swallowed something she was chewing on, and damaged her intestines. I am only supposing here but that is a likely cause, and not a good one. Take pup to the vet please and have her properly diagnosed. Very difficult to do over the internet.

I'll second that, blood in the stool can be caused by anything from parvo to parasites.
A proper diagnosis by your vet is in her best interest.

I'll third that. Only a vet can tell you what's going on, and a vet is definitely needed at this time.

We can only guess. We can't diagnose.

Vet now.

Good luck.