She moved to the left before the process began, presumably to ensure she wouldn't get outflanked by a liberal challenger. Outside of TPP I haven't really seen any major differences between the two on current issues. Of course Bernie is more liberal but both want to raise the minimum wage, both want higher taxes for the wealthy, both support immigration reform/further executive actions, both want to get rid of Citizen's United, etc. I'd imagine Hillary's people recognize these positions don't hurt her in the general election so fuck it.
That being said I eagerly await Jennifer Rubin's #hottake that Hillary is being pulled to the far left just as Romney was pulled to the far right and there's no way she can win a general election.