Mild Ebstein anomaly might never need treatment; there seem to be standardized surgical procedures to treat severe cases, even in infants.
Is the hospital saying the defect is so bad as to be inoperable? What would preclude putting her on a transplant list? Does the baby have other medical problems, brain injury or a chromosomal abnormality?
My cousin’s child has Down syndrome and was born with tetralogy of Fallot defect; they had to let her grow a few months until her heart was “as big as a walnut” before surgery to correct.
She probably has chronic lung disease as well, and sadly, that could be fatal even if she could withstand surgery for the heart problem.