Seedling trees don't necessarily carry all the traits of the parent tree, so this individual might not be as disease-resistant as the "mother" tree. Elms are vulnerable to several pests and diseases (including a virus-like organism), and some pathogens would need confirmation via testing at a plant diagnostic lab. The description of extensive yellowing and leaf shedding is not a good sign, but can be hard to diagnose by itself.

A certified arborist should evaluate the tree in person, and might also be able to take samples for testing if the symptoms suggest certain issues. Some arborists have better diagnostic skills than others, so you can ask prospective hires if they have experience diagnosing elm conditions. Arborists won't be able to treat or cure every condition (as several are incurable), but they can help narrow-down a diagnosis as well as look for sources of tree stress that might be predisposing the plant to a pest or disease outbreak.

Miri