The form Tabea was used in the Luther Bible (before a great renaming took place in 1984 in order to unify biblical names over all translations)---it is the full form of the name in that translation. [noted -ed]
"Tabea" seems a bit pretentious in sound to me-- but undoubtedly a quirky-cute nickname for "Tabitha." I wouldn't personally use it... in the United States the pronunciation would be so mercilessly butchered, in such ways as: Tab-Ee, Tah-Beyh, Ta-BEE-Ah; among others.It would certainly be charming on a little German girl, though. It holds a young, classy, petite elegance.