<human>: Can you succinctly summarize the text in 1-3 sentences?

Our 12 year old rat terrier has had three bouts with "gastroenteritis" since this spring. Our vet thinks it's due to her eating something that disagrees with her. We keep a pretty close eye on her and the other two, not saying she couldn't have found something in the yard and gulped it down. 
Mostly she gets the bloody loose stools, minimal vomiting and she doesn't feel like eating. The first time she was pretty dehydrated and ended up in the clinic for about 3 days.
This time and the time before they just gave us 7 days of 250mg Metronidazole tablets and a bland diet. They suggested keeping her on the bland diet from here out. We have used canned hill's prescription i/d but would like to do a dry kibble if we can find one.
<bot>: Need suggestions for sensitive stomach, dry food for senior dog who has been treated for gastroenteritis three times since spring.