FWIW, seeing it's a Maple, those guys will take a beating and survive, in late-Jan this year I grabbed two ~15-20' swamp Maples from nearby my place, taking maybe a 3cu ft root-mass with me and chopping them to 2' stumps to be containerized (first step in making a 'yamadori bonsai' via trunk-chop method, basically this creates an espaldier style re-growth and you simply remove most of the buds then train the rest which eventually become your bonsai's primary limbs and which, on the top-most shoot, you rely upon for its collar's growth to roll-over the chop-wound you gave it upon collection!)
If the tree's got value for her it's probably at least worth trying to preserve, if it fails you can always drop it later (I know, it'll be weaker / more dangerous then, but it's something you can gauge pretty well so you'd be able to know it was dead-but-not-decayed and make your move then if that was the case!)