How much money should my wife give her friend?

My wife works for a company that has a tool reimbursement policy. That is, the employees can spend up to $X dollars per year on tools, then submit the receipts to the company and get a check for the $ amount spent.

My wife had an unused balance. A co-worker/friend, whom had used her own balance, went and bought more tools, but since she had no remaining allowance couldn’t get reimbursed for them. She gave the receipts to my wife to submit. My wife will get a reimbursement check for tools that she didn’t buy and doesn’t have. The co-worker/friend has them.

Now my wife is thinking that she should share part of the reimbursement check with her friend. She asked me how much she should give. I explained that on one hand she had given up part of her right to get free tools, and if she gave the friend all of the money, she was allowing the friend to use her to get free tools. But, there’s also the scenario that my wife may not have used the money, in which case it would have been forfeited. If my wife gives part of the reimbursement money to her friend, they both benefit. How much should she share? Does half seem fair?