What could possibly cause my healthy 9 year old husky mix to weigh only 27 pounds. She has always been thin and now I guess I am starting to be concerned by this.

I don't know much, but I 'd like to ask if you give medicine to your dog to remove any potential worms? Like tapeworms. These usually reside in the dog's intestines and eat up the food, instead of giving it to your dog.

Also, have a look at the thread:

https://www.askmehelpdesk.com/dogs/why-dog-too-thin-35026.html

9 years old is getting on in years for a Husky...

Time for a vet check to make sure everything is in good working order.