Thank you for trusting your question to JA today. I am a licensed attorney with over a decade of law practice and over 20 years of experience in the legal field. I’m happy to be of assistance.
Unfortunately, you'd be fighting uphill here. Your state's courts are going to look at things in a way most favorable to the employee. This is because you, as the employer, have the power to draft your policies in a way that is favorable to you. You have the stronger position in terms of negotiating employment terms, and setting your company policy, which the employee would just have to accept.
Because of that power that you have as an employer (whether you choose to use it or not), courts and the labor board will use that fact against you and find in favor of the employee when issues are ambiguous.
That is not to say that you can't argue that she was already paid for her time off. You can claim unjust enrichment, showing that she was paid for days off that she took. The court will either accept it or they won't. It is a valid legal argument, but the court isn't bound to accept it. It at least gives you something to argue, if you wish. Furthermore, you can point to the fact the Federal Department of Labor specifically allows for the deduction of time off from accrued vacation.
The more important thing here though is to redraft your policies to include that time off can be written out of vacation by the employer, whether submitted by the employee or not.
If you have any further questions, please let me know. I invite follow up questions, so use REPLY for those. If you have no further questions then good luck going forward and please do not forget to rate my service with a top-three rating so that I receive credit for working with you today. Please rate me based on my service and not on your satisfaction with the law, which I am not in control of and I am just reporting to you. Also, feel free to request me in the future, if you have questions concerning a different matter.