Looks like their "Adult" food has brown rice and their "grain free" has carrots and peas but they're pretty far down on the ingredient list
The Seafood Medley Grain Free canned comes up as 2.3% on my carb calculator, but that's not very accurate.
I'd say if it looks like it might be something Phoebe would like, buy a can or two.....if it spikes her BG, you'll know it's too high for her (but maybe keep a can around for PJ parties)
One can of any food isn't going to cause any permanent damage....it all works it's way out!