Also, it seems in your kind of a scenario it would be difficult to avoid the 'unlimited vacation policy'-type problem, where ultimately it is still at the final discretion of one party. So realistically, there is still some portion of the pot that she is free to spend at her discretion, but it is implicit. Would it not be better for everyone to just make it explicit? Is that not a red flag, since by not explicitly designating some funds as hers / not transferring them into her account to use as she sees fit you are maintaining more control of it and how it is spent?
To be clear, I am not talking about your situation in particular of which I know very little, but presenting more of a general hypothetical argument.