OP with a quick follow up to share what I've tried doing when this happens:
--playing with wand toy, thinking she is meowing out of boredom. She no longer plays with this toy or most others... she might engage for 1-2 minutes, so not long enough to wear her out.
--picking her up and petting her a lot, thinking she just wants attention. This works while I am petting her, but after putting her back down, the wandering around and loud meowing resumes.
--ignoring, based on advice I've read online. Again, this doesn't seem to work as she'll continue roaming the house and meowing.
--giving her a small amount of an OTC calm supplement (about 1/2 a kibble) -- it's this one:
https://www.chewy.com/pet-naturals-calming-cat-chews/dp/118787?utm_source=google-product&utm_medium=cpc&utm_campaign=f&utm_content=Pet%20Naturals&utm_term=&gclid=Cj0KCQjwyZmEBhCpARIsALIzmnIN4-kOOEXZ_WF9yPX69xjQKM9MEvTpcShcXrICoZ0imvRv_cO0tLMaAmVyEALw_wcB