Well, since "Sabrina" isn't derived from a slavic word or name, but it comes from the latinized form of Severn, which is a Welsh river, in Bulgarian, "Sabrina" is again "Sabrina".
The Bulgarian word for 'Thank you' is:
Blagodaria
However, it is not written like that, but it should be written in cyrillic letters. So this is how it should be written:
благодаря.