Dropping counts can be a sign of relapse. They can mean any number of other things, as well.
These are significant drops, so it's good the doc is doing the BMB to make sure there's no relapse. But, again, a lot of things can drop counts. Mine started dropping about three years out. No one knows for sure but it looks like there a decrease in the cellularity (blood cells in the marrow compared to fat cells) might have been the culprit.
No one knows why it dropped and my last BMB showed it back to normal levels. My counts seem to be coming back up, too.
While that's pretty rare and I'm not suggesting that's what's happening to your mom. it does show how far out counts can drop and how varied the cause can be. As for CMV they probably told your mom if she tested CMV positive or negative before the transplant. If she tested negative and the donor was negative, it's not an issue.
Blessings
