IS there a way to get a history of edits on a character sheet? I believe I have a player who is cheating and added something to their sheet after the fact.

I have locked down the sheets now.

No, RPoL doesn't in general track edit histories (with the exception of the wiki).

At the bottom of the character sheet page, tho, you can find a statement saying when the sheet was last edited (time and date) and by whom (player or GM).
This message was last edited by the user at 15:52, Mon 30 Mar 2015.

You might try reserving a thread to hold "current" copies of the Character sheets.  to compare to what is current now.

In reply to C-h Freese (msg # 4):

Yep, make yourself a thread with a copy of everyone's sheets.

AS a player I also manually add edits with comments at the bottom of the sheets. The OP can ask that his player do the same to avoid any confusion.

Example:
3/25/15 - changed starting language with DM's approval
3/28/15 - 1 potion of CLW
3/29/15 - added level 2 alchemist, added ant haul extract, added +1 leather