I don't think that is her monogram. Her cypher is EIIR; Elizabeth II Regina. I would expect her monogram to be an entwined version of that, not just an E; ER at the very least.
Neither do I think the crown is the right one; looks more like the one from Prince Charles' coat of arms.
I suspect what you have is something monogrammed for someone whose name began with E, the monogram of a non-British royal or a marketing ploy.