Possibly Just Stress?

I just rescued a 6 month old chihuaha/dachshund mix named Lucky and brought him home to my nearly 1 and a half year old toy poodle mix, Coco. Coco is a bit high strung with humans, but loves to play with other dogs. And Coco welcomed the new puppy very well. They play together often (rather roughly... on both sides), but they love to play. Coco, however, does resource guard a bit--with toys and bully sticks. I'm always watching when toys or bully sticks are around to make sure nothing goes too far, but Coco has snapped at Lucky a few times. No contact, just Coco saying, emphatically, "get away." Lucky, unfortunately, can be annoying. I understand why Coco is saying, "get away," because sometimes he just won't back off. Sometimes he will roll over to say, "I'm not a threat" when Coco growls, but other times it seems as if he's determined to be as annoying as he possibly can to her.

Anyway--I get that Lucky is a puppy and that I need to watch them carefully. Right now they are separated when I'm away. Most of the time they love playing with each other, so I don't believe there's a DA issue here. Just an adult dog getting fed up with a puppy's behavior. I write this as a background for Coco's issue.

About 3 days after Lucky came to live with us, Coco woke up seeming like she wasn't feeling well. I took her for her morning walk (alone) and she pooped quite a bit. When we got back, about 20 minutes later, she pooped again on the carpet. Most of the poop looked normal--one looked like perhaps her digestive track was a bit irritated (clear gel-like substance at the end of a poop). I have a doggie door that goes out to an ex-pen. Coco could have walked 5 feet to get there, but she chose not to. It took her maybe half a day to return back to her hyper self.

After this incident, everything was fine for another week and a half.

Then, this morning, Coco woke up seeming like she wasn't feeling well. I took her for her morning walk and she pooped a lot. We got back and then, 20 minutes later, she pooped again on the carpet. This time all the poop looked normal. And immediately afterward she was running around and playing with Lucky.

Strange thing is that Coco doesn't poop a whole lot normally--just small amounts. But on these two days she pooped... a LOT. Mostly normal poop, just a lot of it.

Just stress because of the new addition? Could she be holding in her poop? She's not eating more than usual (it's been so hot she's actually eating less, but still eating at least one full meal a day). Could it be something medical? She's active; doesn't seem depressed. She's up-to-date on all her vaccines (the new puppy isn't fully vaccinated yet and is on anti-biotics for tick bites).