One of my best friends was named Shaina and she was from Pakistan. She pronounced it Shah-Ee-Nah. Shah and Ee are tied together, short and are suppose to flow. It's as if the "i" had to dots on it.
This is my name and it's pronounced Shay-na. Also it's true that it comes from Yiddish origin. The majority of people with this name spell it Shayna. I was also born in 1997.