I always had like 3 Ashley's in my classes from Kinder to 12th, personally, it sucks more when you're having to be called Ashley *last initial* because there's to many of your name.
Either way, the nicks for Merrina are Meri (like Merry) and Rina. I've called her my little Rina enough to figure that I'll prolly just continue to call her Rina and never Meri.