If it's one particular place the dog is marking, block her access (things like laundry baskets work well for chairs) and make sure to clean the chair thoroughly with an enzymatic cleaner. I would hesitate to read so much intent into her behavior. The marking and chewing are probably just signs of her insecurity; she's in a new place, her people and most of her things aren't there, and she isn't sure what resources she needs to protect or what the rules are. It's not surprising that these behaviors weren't immediately apparent and only emerged after a couple days. Animals often go through behavioral changes as they become accustomed to a new environment, and the first reaction is often to shut down, which can appear similar to good behavior, but is really just the animal withdrawing from the environment as a defense mechanism.
I'm not entirely sure from your post what the issue regarding the toys is. So long as her toys aren't unsafe, I wouldn't worry about them being well-loved. My little dog's favorite toy is a (formerly) stuffed hedgehog that she eviscerated over the course of a couple years. She loves it to death (literally), and since she still enjoys it I have no intention of getting rid of it. If you're concerned about her destroying your dog's toys, I'd just put the softer toys away for the duration of her stay and let her play with her own.
As for updates, unless there's a health or safety issue, you can just let the owners know that she's been a little anxious in the new surroundings, but that you're working on making her feel comfortable. Add specifics if you wish, but emphasize that her behavior isn't unusual (it isn't!!) for a dog in a new environment, and let them know what measures you are taking to help her settle in.