Endorsements vs Voting Choice

I just saw an interview on MSNBC with CA Senator Barbra Boxer who has yet to endorse a candidate in the democratic race. David Gregory went out of the way to mention she hadn't endorsed in hopes of obviously getting her to crack. However, wouldn't it have been easier to ask her who she voted for? Unless she didn't vote in the primary she clearly voted absentee (since she is in DC) and so it shouldn't be that hard to say who you believe in... provided she wants to be honest about it and not just someone who is calculating and kicking the can down the road against making a call to soon in a tight race.