One of the things to remember about the personal reimbursement provisions, as well as the "salary" stipend allowed in the law is that it is written to the benefit of the candidate ~ else there'd be a lot of Senators in prison and we'd be running new elections for their replacements all the time.
The candidate doesn't have to provide any "proof" beyond that specifically required in the law ~ to wit "a log". It's up to the public prosecutor to prove that any one item was disallowed.
The FEC doesn't do that.
This is going to be tangled, considering the revolving door of personnel she's had on her campaign and as "treasurer" (for those times she was actually following the regulations and had a treasurer, that is).
There are a lot of Senators that should be in prison. Most of them I reckon.