Puppy Urination

Question
I have a 3 month old Beagle puppy that is very smart. For the most part she knows to go to the door and sit there when she has to go potty. She will go days without having an accident inside. The problem occurs when my brother brings his girlfriends 1 year old dog over to our house. Initially, they play and behave themselves. However, out of nowhere, she'll just pee and walk away and continue to play. And it's not a little puddle there is a good amount. She will do this multiple times within an hour and without even showing signs that she has to go outside. I thought it could submissive urination but she doesn't cower, put her tail between her legs, or flatten her ears. I know you are suppose to take puppies out after intense play (while we play with her she'll go to the door when she's ready), but why is it so different with a dog? Are my expectations set to high? And, finally, is there anything i can do to stop this behavior? Thanks!

Answer
Puppies also pee with excitement so this could be the reason.

I suggest that until she is older, keep their play time outside.

She is obviously so happy and having so much fun, that to remember or want to leave the game that she forgets her house manners.