You're going to encounter a few people on this forum who have had to switch oncologists to find one they mesh well with. I guess the trick is knowing when to jump ship. You don't want to abandon a good one over something small, especially if it's close to home. I don't think a good oncologist would be offended if you sought a second opinion, but if you're not comfortable sharing that desire, you can always seek the second opinion without their knowledge. However, it takes time to get that second consultation, meaning you need to start early so you can actually have it in an actionable time frame.

With the pancreas, you can't afford to fool around. Everyone should be striving to be seen at least once by specialists at a center of pancreatic excellence. If you're already at one, you (your mom) might choose to just stay with them, but be aware that there is a huge diversity of opinions and several treatment options at different centers.

If you're actually getting more CA19-9 and other bloodwork done in 2 weeks from now instead of a month from now, that's probably often enough for now. I wouldn't leave a good doctor solely over that, but I did leave a local generalist oncologist who was testing my CA19-9 monthly while I was on biweekly Folfirinox for a specialist 2.5 hours away who is testing it every two weeks along with my new biweekly post-Whipple chemo (Abraxane + Gemcitabine + Cisplatin), and I don't regret it at all. If your mom's CA19-9 increases on the upcoming test, that alone should be a call for much more aggressive action, at which point you can make those wishes known to her oncologist again.

As I've said several times here, you might get the same drugs at different providers, but you don't necessarily get the same care, skill, expertise, facetime, or communication as you might get elsewhere. It all matters. My dad (RIP last week) chose a hometown generalist to treat his mesothelioma and paid a very heavy price. 🙁 At age 85, it was hard getting him in a true, fighting mindset, and your mom might be a similar case.

Even if there is "no discrete mass" on imaging, there could be "MRD" (minimal residual disease) circulating in the bloodstream, and one of the tests based on ctDNA (circulating tumor DNA) should be able to pick that up.

Get as many of your options as possible locked and loaded to fire in parallel, so everything is in place when you have to make that next decision. It may help avoid things being dragged out serially for too long.