Question: What happened to Dinah (Gen 30:21)?  The last time we read about her is when Jacob and all his descendants enter Egypt, at the end of Genesis (Chapter 34).  When Exodus starts we just read about the 12 tribes of Israel.

Answer:  We are not told in the current accepted Christian texts of the Old Testament what became of Dinah, the daughter of Jacob and Leah, except that she went down into the land of Egypt with Jacob and her extended family (Gen 46:6).  In Jewish rabbinic literature, there are various surmising and lore, however we cannot validate any of it by scripture, so we do not ascribe to any of the conclusions.  There is an interesting article at https://en.wikipedia.org/wiki/Dinah which may provide some insight.  We make no recommendations as we are not given that data in scripture.  What we do understand is the whole episode is a tarnish on righteousness and Godliness.  It shows events and outcomes that may occur when we allow worldly desires, corruption and political or economic gain to shape our ethics and principles.  One point is clear, Dinah and her family were more than likely absorbed into, and represented in one of the 12 tribes at the Exodus.