First things first - check her for a UTI. You should be able to drop the sample off at the vets if cost is a concern (therefore avoiding the visit fee unless the test shows a problem and you need to bring her in).

If that checks out ok, it's most likely stress. Even good stress and excitement is still stress, and a new housemate is a big change. And if they are playing together that stimulates the bladder/bowels, so she may not even realize she has to go out. I'd take her outside for potty breaks more frequently and watch carefully for potty signals (circling, sniffing, whining, etc.). Some dogs can be quite subtle in their signals - one of my dogs will scratch at the door, while the other will just stand up and look at me (took me a while to get the hint!).

I've been there, done that.

I have three large females, the youngest was brought into the house two years ago. Because I already had a total of three females a few months prior to the pup coming along, I knew very well what I was getting myself in to. I was fully prepared to do what was needed to stay on top of things.

I would rule out a UTI and watch for potty signals. Stress is probably the problem, but one never knows.

I've house trained many dogs, and it's my opinion (not shared by some) that pee is pee, and poop is poop. When it's in the house, it stinks and stains.

A systematic approach to house training is best, that way you know what is going on.

If this continues, and assuming there is no medical issue, you may find yourself backing up completely and starting all over in the potty department for your older dog. After all, she is three years old, but acting like a 3 month old pup.

Good luck!

SG

Congratulations on your new arrival :)

Stress and excitement are good candidates for reasons. It's an exciting time to have a new playmate around 24/7. Keep a close eye on them when they do go outside for a potty break.

We've fostered and doggy-sat a few dogs now and our pup LOVES having company; however, just like a little kid sometimes all that fun means he over-looks the important things like eating, sleeping and going potty!

Our little guy would be having so much fun romping around outside with his new buddy that he'd forget to do his business. 20 minutes later he'd be in a panic to go out OR just not make it. Entirely our fault for watching the wrong dog!

With one particular foster it became a matter of separate potty breaks before playtime -Just to make sure everyone did what was needed. Just waaaay too much puppy play energy and nothing got done, so to speak.