If she is alive she survived being squished under a ton of molten rock...
Remember, Harry survived being similarly-buried, in the duel vs. the Ick & the Rampire (in the Erlking's hall). So I don't doubt that Jim might conceive a similar scene for Hanna's survival.
The other bit of "Harry Did it First" lore I find relevant is how Harry used his Fuego spell (twice, that I recall) to insta-chill things: an ice-slick under Scarecrow-fetch's feet, and an ice-bridge in the harbor, to escape the ghouls' assault.
Harry says that it's just the physics of the spell, which grabs ambient heat and concentrates it to make fire for him; all he needed to do was concentrate the area the heat came from, and he got an equal-and-opposite freeze.
So I don't doubt that Hannah's fire-skills (which are better than Harry's) could have formed a cooled and
solidified-rock shelter out of the falling
molten rock.
