I just noticed that my older girl is still swollen and has blood although it is over four weeks since her heat started. My boy dog stopped paying attention to her a week and a half ago so I assumed she was finished. There is no smell to the blood. I can't think its relevant but her daughter is just starting her heat. Obviously I will keep an eye on it. I'm a bit concerned as she hasn't been on this long before.

Sounds to me like her daughter is extending her heat.
Just like with people if you are around another person long enough your cycles start to go in sync.

Usually a dog will bleed up until day 10 of their heat, this is when they are ready to mate. Their actual heat lasts for 21 days but there is little or no blood during this time.

Just keep a close eye on the discharge, if it changes color or starts to smell bad make sure you get her into the vet asap ;)
Sorry to bring up a horror story but my mom had a girl who was 6 years old when she went in to be spayed, she had a severe case of pyrometra, the vet said if she had have been spayed even a few weeks later he could have died... there were no symptoms at all.

She might be pregnant. I'm not too sure. Ive only bred one dog in my life. That dog had weird discharge that was red. Vet told us she was probably bred. Brittie also did her heat cycle by the book. It was a very long month... and she would come into breeding heat at the very sight a male dog. She only had one litter, but she loved babies. I hate to say it, but she would have enjoyed being a puppy mill mom! Lol

I did wonder if it was something to do with the youngster coming on which is why I mentioned it. The first thing I thought when I noticed was pyo but I've always understood that the discharge is smelly and the dog would appear unwell. To hear that there can be no symptoms is very worrying. I'll prob get her to the vet to check. My boys reaction to the little ones heat is unusual. She has only just started to swell and has no blood but he is trying to jump on her already. He doesn't normally pay any attention for the first week.