The term polymath is very similar to Renaissance man. They're almost synonymous. Translated from Greek, polymath literally means having learned much. Generally, a polymath is a person of wide knowledge or learning. Filling in the blank in your example sentence:
Mrs. Jones is a real polymath. Although she teaches Spanish, she can tutor any student at our school in any subject.
I think that the term erudite is a good word to describe someone who is well-read and knows a lot of things in general, but not necessarily someone who is an expert in a variety of different subjects to the extent that they can actually teach them.