What's the most likely diagnosis? Patient presented with an enlarging

What’s the most likely diagnosis? Patient presented with an enlarging, painful ulceration on the lip that developed over the previous 2 weeks. She had a history of myelodysplastic syndrome treated with azacitidine. History was remarkable for peripheral blood stem cell transplantation for myelodysplastic syndrome 1 year earlier. Physical examination found an ulceration of the right lower mucosal and vermilion lip extending onto the cutaneous lip, with overlying hemorrhagic crusts (Fig 1, A). She also had erosive papules on the hard palate. The remainder of her examination was unremarkable. Tzanck smear found multinucleated giant cells (Fig 2). The lesion continued to expand despite valacyclovir treatment for 7 days. (Answer and link in 24h, JAAD Case Reports)
A. Labial necrotizing fasciitis
B. Herpes zoster
C. Paraneoplastic pemphigus
D. Treatment-resistant herpes labialis
E. Mucocutaneous histoplasmosis