If you link her MDX to your MDX account, your open FP booking window becomes her booking window, too. The only thing is, one of you would have to be included in the FP grouping for the day she is using her Guest Passes for you.
The CM can include an onsite guest in the FP group, remove them when the Warning pops up, and then complete the FP booking using your open booking window.
Sorry still so confused. Do you mean that one of us would have to already have paid admission for the day and then the guest passes can be added to the fp reservation more than 7 days out? So that in our case, since we only have guest passes for this particular day, we would only get the 7 day window, even though we have a WDW room reservation that includes the guest pass day?