i would say she's lying,but I'm not sure...

Dogs, if tired, hungry, thirsty, etc, will often try to find trash on walks. If you let them eat it, they walk slowly for awhile, making them seem sick. Also, once you're back at your house, if you check under "last eaten" on their stats, the trash comes up as many exotic things - I.E. spaghetti, popcorn, and of course probably meatballs. No idea about the pink powder, though, so probably just a lie. My cousin did the same thing and told me it rained once in his game (there's no real weather in Nintendogs...)