Skulltitans are notoriously hard to kill without the proper technology, and this one has been bolstered twelvefold by the levels of radiation present.
Waiting for an opening would be a dangerous game. Jentha's unbridled power could spell immense disaster for herself and others. Plus, your intruder could decide to retreat deeper underground with in tow.
Utilizing alchemy to incapacitate the creature is also too volatile of a method, and could risk as much harm to the Holder of Mind as letting her get swallowed whole.