Park Day Adjustments After FP+ Selections Made

[stinkpickle]

I know that a visitor can only make FP+ selection for as many days as are on his/her park ticket. BUT, if the first day of the ticket ends up getting used outside of the pre-selected FP+ dates, what happens to the FP+ selections, if anything?

Here's my scenario...

My family (we all have APs) is bringing my niece along on our next trip. We purchased a 7-day hopper for her. Due to airfares prices, we are actually going to be at the resort for 9 nights. When our FP+ window opens, I plan to start at the last day of our trip (better chances for FOP) and work my back towards the first day. I will only be able to make selections for her last 7 seven days. Now, let's say we arrive at Epcot on day #1 planning to add 2 days to her ticket at customer relations inside the park. Will her last day's FP+ selections get dropped as soon as she enters the park? Does that make sense?

 

[DisneyWishes14]

Why not just add the days at Guest Services outside the park prior to entering on your first day? Then, upon entry, she will have 9 days of valid tickets and there won't be any FP+ issues on any days.