Ella's adorable~! None of my dogs has ever refused food just because their tired, but, if they're not feeling well, they will. My dogs and Kids and I did a 13 mile hike this Spring, and both dogs layed around doing absolutely nothing for about 1 1/2 days afterwards, but, they still ate (they're piggies that way). It is possible Ella pulled muscles on her walk, and because of this isn't feeling well. Is she drinking water and staying hydrated? If not, you might want to have her checked. If she's drinking water, I'd probably wait a day or two before worrying too much.
Good luck, I hope she feels better soon