Tell her you're a big boy now, and can make your own life decisions, thank you very much. If she doesn't stop, let her know that your relationship might get 'ugly', without being too specific. Deal with it head-on, otherwise she will only question why you haven't answered any of her emails, and still not get the point.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma