I've never heard of Magnolia salsa - do you mean Magnolia 'Susan'? Also, do you mean the tree is only 12 inches tall after 19 years, or did you mean its 12 feet tall? And do you mean its only 3 inches away from a building, or feet away (feet= ', inches ")
On the assumption you've got your symbols mixed up, its not impossible that a 12 foot magnolia 3 feet away from a building could cause problems with the foundations, but not a foregone conclusion either. If subsidence is already present, the only way to be sure what's caused it is for the architect/company responsible for the work should sample any roots present near the damage and send them to the labs for ID - which is what they do if there's an insurance claim involved.