Humm. Don't know about the potty issues, maybe someone else has some better advice on that than me...but I will comment on the dog walkers
We have a dog walker that we use for Brooklyn if we are out all day, late or something (I am not working at the moment, but I had a all day 3 week course a month ago that we used her for too). We love her. But, I interviewed about 10 people! I wanted to make sure Brooky just wasn't going on one of those massive walks with 10 dogs. This woman we hired comes over for just a play and potty with Brooklyn (no walk), or takes her for a walk or picks her up and take her with her dog and no more than 3 others up to the reservoir damn where then can at off lead too. The best for the evenings or when Brooklyn was just a puppy was when she would just come over and hangout with her for 30 min and take her out back to pee. Sometimes we don't need a full walk, just someone to stop by do a potty break and some play time, that is cheaper and might be something to look at as well if you think she is getting enough exercise
it's all about finding the right person, a good one will come over to your house first to meet you and Coco.
During that full on three weeks I was away too, I took Brooky to daycare one day a week as well (but again, interviewed a ton of places!). I ended up taking her to a daycare that was further away because it was just so much more calm and for small dogs only...the owner has a cavvie and there were a few others there to. It was just a chill, calm, fun environment...that is key with daycare because you dot want them picking up bad habits. Daycare is expensive though, so once a week or once every other week worked fine for Brooky.
Oh. Now that I think about it too, when Brooky was having some potty issues a month back, our trainer helped us to understand that our stress around it, not the we showed it, but what we were feeling on the inside, was actually contributing to Brookyln's stress which then made the problem stick around. I would never let her see me, but it is true on the inside I was like "what the heck??" because it was such new behavior. When she pointed that out to us and just said "Let it go. If she goes inside (but is in her "proper confined place), she goes inside. She will grow out of it again, but the more nonchalant about it we are, she will follow." And it worked! Took about a week, but I think our internal anxiety over it just fed into her own. Now sometimes, if Brooklyn is in one of her "moods" and won't go potty before we leave in the morning (or not going as much as normal...I.e. The fake pee for a treat!) then I just smile and say oh well. Put a pee pad down with her behind the baby gate and go on with what I planned for the day. She doesn't like to go inside, so eventually she realizes "oh, mama won't just stand out here longer if I don't go, I still have to go inside after 30 min". Do you have a pee pad or anything that you put in the pen when you go? I wouldnt make the space smaller as of yet, unless you are going back to crate training 101 (letting them out every hour like when they were pups), because she is obviously going to soil the space if she if left alone for even a little while (might just be adolescent regress that will pass if you go back to basics a bit, we did that with Brooky and since inside she already knew what to do, we weren't in "basics" again for very long). What about attaching your x-pen to her crate with the crate door open? And a pee pad in the far corner of the x-pen?? Like back to the basics for a while 'a la Ian Dunbar'?
This might not be what you are dealing with at all but thought I would throw it out there just in case!
Good for you for ruling out bowel and urinary stuff with the vet too!!