Ok so I feel really dumb for not noticing this sooner... but Riley has a tiny, silly floppy little dew claw on one of her hind legs. It's seriously so small it looks like it should belong on a chihuahua. I guess we never noticed it because it's buried in all her fluff and she's never been shaved down. We really only noticed it because the nail on the tiny claw (which doesn't appear to be functional) is super long, I thought it was a piece of stick or something caught in her hair.
Anyway other than keeping the nail trimmed anything to watch out for with these things? I didn't even know dogs could get rear dewclaws. After some research it seems to be common in large/giant breed dogs of Scandinavian origins (which makes sense since she's half Bernese).