Lol, I thought Serenity was going to be a lot fatter from how you said she felt! She looks fine if you're not going anything high impact or crazy active. I can't believe you can't feel any bone though? Anyway, on a short coated dog, I generally like to see the last few ribs when they're moving, at least. But much comes down to personal preference, the individual dog's build, and activity level.
She certainly doesn't look unhealthy.