There is also nothing inherently shady about Meghan preparing her 2019 U.S. return with an MFS filing status. It's pretty rare for a married person's liability to be less as a single filer than as a joint filer, but her particular tax position may have been one of those cases. The IRS actually encourages married folks to figure their tax both ways (on a joint return and on separate returns) to ensure using the filing status that results in the lowest combined tax. The IRS also says that once you file a joint return, you can't choose to file separate returns for that year after the due date of the return - which would seem to discourage changing lanes on a regular basis.
I'm also pretty sure that Meghan is relying on someone a whole lot more versed in IRS publications and pronouncements than I am for tax advice so take all that for what it's worth.