Is that legal?
(Not that it matters to the Clintons)
The FEC regulates how politicians can use excess campaign funds, so if she reported this to the FEC, it's either legal or they can tell her why it's not.
There are quite a few articles online that specify what politicians can do with excess campaign funds but it's hard to find one that fully covers all the different cases. Here's a couple:
What Happens to Leftover Campaign Funds When a Candidate Drops Out?