Meringue is droopy now that I’ve added vanilla— how can I save this?

I whipped my egg whites and sugar (as per Swiss Meringue) to fairly stiff peaks, and added vanilla as per the recipe and now my meringue is droopy and I can’t get it to whip back to stiff peaks. Can I add some cream of tartar or something now to help it to stiffen up again? Should I just keep beating it some more?