Either, in that sentence, is the equivalent of too. Too goes with a positive statement and either with a negative one.
it was lost on Mrs. Trollope too
it wasn’t lost on Mrs. Trollope either
So that's our guide on where to look for the answer about the comma. Back in the day, I was taught a comma was required before too, but that's wrong.
The comma is optional. Using one gives too/either more emphasis.