Yard trained but not walk trained

Hi! I adopted a lovely 4.5 month old cavalier king charles spaniel just yesterday. Her owner said she’s house trained, and everything I’ve seen so far agrees with that—except that she refuses to pee or poo on a walk. Her last owner had a yard that they would let her wander in, and unfortunately that isn’t a possibility when living in an apartment.

She had a single accident last night, but held it in for hours, despite me taking her for multiple long and slow paced walks that day. Her body language made it pretty clear she felt badly about it too. I cleaned it up thoroughly (no negative reinforcement ofc). I thought that it could just be a new and exciting environment, new people, and adjustment to walking on a leash.

Today, I’ve taken her out probably about seven times, for lengths of time anywhere from 10 minutes to nearly an hour. I’ve kept her on the same three small blocks, so not introducing anything new environment wise (besides the cars and people that come with living in a city). There are a variety of locations—wet grass, dry grass, turf, dirt, rocks, gravel, concrete. Her last owner said the yard was full grass, but it doesn’t seem like that’s doing it either.

I have sat in front of spots for a long amount of time hoping she would just go, but she refuses to the point of actually lying down. We’re now looking at 7:30pm my time, and she hasn’t pooped since at least 2:30pm yesterday, and peed a small amount last night once. At this point, when I take her inside she is clearly looking for a place to relieve herself (pacing, smelling the ground, getting ready to squat) pretty much immediately—I keep scooping her up and running her outside, but then she refuses to go.

Pretty positive it’s a case of new environment, distractions, not realizing the connection between relieving herself in the yard vs. on a walk, etc. and those are all things I’m happy to work on with her, I just really want to know how the heck I can get her to actually go outside so I can get her started on retraining. I’m dying here and really don’t want to take her inside for her to have an accident.