Hemp (not given to dogs, period). CBD oil varies as to QUALITY, and is not usually recommended by vets as little to no testing has been done on it, relating to dogs or pets.
Your vet’s advice would be needed, as to whether it was advisable (how much to use – if so) and what brands or brands were best for dogs. I also wonder WHY dog has not had any medical work-up on why it is anxious since a dog who is nervous or has anxiety may have pain of some sort (in addition).
Chihuahua should weight 2-6 pounds, NOT anything LIKE 21 pounds!!!!! If you have a MORBIDLY OBESE dog; see the vet, ASAP, because it is likely in pain and also very likely to develop multiple health problems including DIABETES – which is fatal, if not treated.
Interesting…. YOU do not indicate your dog has had any veterinary medications offered (for this situation) nor do you indicate any OTC treatments (like Anxiety drops or Bach’s Flower remedies, or acupuncture) having been tried, and the outcomes, from such products.