Occasionally I look after 4 chihuahuas. 3 of them are always 100% fine, but the 1 dog is timid/anxious/fearful. When the owner is there, she is ok though still timid/shy, but as soon as the owner is away, she stays practically glued to her bed and hardly eats, and usually won't go out, and I can't touch her since she'll try to snap/bite me. I can sit or stand near her though. She is not very food/treat motivated though I have tried winning her over softly softly that way and by sitting near her and avoiding eye contact etc. She's often not interested in a treat at all. When her owner returns she is like normal and far happier again, as if she just instantly snaps out of it again.
When the owner leaves, she does not bark or get visibly anxious or whine like a typical dog with separation anxiety, strangely she'll "accept" that, but then soon goes to her bed where she stays.
Any ideas for what I can try except telling the owner to get a trainer? All I can think of so far is to try to experiment with getting her more comfortable with me when the owner is still at home, when she might be feeling more safe or trusting. - and possibly to suggest trying a thundershirt, anti-anxiety medication or these dog relaxation pheromone sprays.