When you make the reservation, be sure to check and find out which show you'll be getting a pass for; they used to base it on the time of the reservation. Guests have reported being able to request the other show time, but it depends on availability, so you won't know until you get there that day.
If you're hoping to see the first show, I would try to get an earlier reservation. BB isn't a slow meal. I'd allot 60 to 75 minutes, assuming you're not going to request a waterside table (if you're going to request a waterside table, then I'd add another 30 minutes just in case the wait is long, but it's usually worth it to most guests). The F! viewing area opens about 30 to 45 minutes before the show starts (I think) and there will be plenty of guests already lined up waiting to get in at that point. While there are good views from throughout the dining package viewing area, the areas closest to the water fill up first.
If this is going to be her only chance to see Together Forever fireworks, I would try to see them from Main Street (or the Castle). If she'll have other chances to see the show, then seeing it from the RoA is fine. I think RoA is good for folks that don't like the crowds and aren't that interested in seeing the non-fireworks elements (e.g., flying characters). From the F! dining package viewing area, you'll be able to see the projections (similar to the ones on the castle) and the fireworks.