I don't think I've ever heard Amtrak dining car meals referred to as
gross before. Unless you are talking about the snack-car meals - just a few notches above airline fare - served on most Northeast Corridor (Acela Regional) trains, this simply isn't an accurate description of any meal I've ever had in the diner (and this includes some remarkably
low periods in Amtrak dining-car history...). That doesn't mean Amtrak, like any restaurant, never has quality issues, and I respect ducklite's opinion of course, but I can't help but wonder just which Amtrak food-service you are referring to.
Each Amtrak long-distance train carries both a lounge and dining car. Full meals are available in the diner; the lounge has "sandwiches, snacks, and beverages" (microwavable stuff, though edible). There is no comparison between the two. One is just a snack counter; the other a real "restaurant", and not
fast-food at that.
Nothing wrong with bringing your own snacks though, as the lounge is overpriced and the selection is necessairily limited. I would also second the suggestion of having activities for your dd, especially after dark (during daylight the passing scenery is the best pasttime, though kids may not be quite as enthralled as yourself). Check all possible baggage and just have a small overnight bag (or tote) with a change of clothes and any other necessary items for the overnight trip in the coach with you (perhaps a second bag with your daughter's activities; and possibly a further small bag with the snacks). There is more than sufficient room for full suitcases, but the less you have with you the better off you will be.
The following link may be helpful, especially if you have never travelled by
long-distance train before:
http://communities.prodigy.net/trains/amthints.htm
Have a great trip!