Large breed dog I’m sitting for shows signs of resource guarding. Do I tell the owners?

I’m doing a week long overnight with a 6ish year old Rottweiler. I did the meet and greet, played with and pet the dog, gave it treats from my hand, the whole thing. It went very well.

The owners also assured me that they are stringent with training her so she’s never had any close calls or incidents around anyone young children included. However, they have also never used a pet sitter.

There have been two occupancies while I’m here that the dog has growled and showed teeth- once I tried to take something from its mouth (I know that’s basically my fault) and another when I tried to pick something up from behind her but she was looking at me. She did not snap but again growled and showed teeth, I assumed by how the owners talked to me that something like this wouldn’t happen?

Am I over reacting or should I mention it to them but let them know we were able to manage?

Thanks!