I do not have a dog, but I recently adopted a cat and then had to go out of town for five days unexpectedly. I had a sitter come twice a day. So this is not super similar to your situation but my point is, I was SO worried for my kitty. She's a very sweet, affectionate lil baby and I was nervous that she would be lonely or scared or god forbid hurt herself while no one was around and then the sitter wouldn't get to her until that night...she was totally fine. We got home and she was her happy, snuggly, sweet little self.
Sorry I don't know more about boarding but this is all to say that pets are resilient little things and your pup will be a-ok. As long as you've done your due diligence and she's staying in a reputable place, which it sounds like he is, she'll be fine. Do they send you updates from the kennel? My sitter would send me pics and write-ups whenever she stopped by to feed the cat and that really helped alleviate some of my anxiety. The whole drive out of town I was super anxious but once I got those first couple updates from the sitter, I relaxed.