She looks purebred to me. Maybe not the most well bred, but purebred none the less.
Many many breeds of dogs can have black spots on their tongues. My boss's bouvier had a few black tongue spots, and this handsome guy:


also has some, and he is a purebred

Irregardless she is a cutie and looks to be fitting in well.....maybe you're that much closer to a third dog of your own....