William,
It is possible that she will be able to make those reservations as well, but it is probably unlikely. The reason I say this is that with the
Tomorrowland Terrace Fireworks Dessert Party, the dates that it is held, and thus the ability for agents (or the website) to book the experience, are rarely posted 180 days out. They seem to go up much closer to the actual date, sometimes just weeks beforehand.
My recommendation is that when she makes her other reservations that she try. There is no harm in that. But assuming they don't have the dates out yet, she should ask when they think they might become available. They may not know, but they might.
Even so, assuming you get no good answer there as well, then do what I do. Set it on your calendar to call every Tuesday (Monday the lines always seem busier), or every other Tuesday, leading up to your trip. Eventually you will get lucky! Everyone else is in the same boat with you, so don't let it stress you too much!
Have a magical (and delicious) vacation!