It's a warm one out today (and I am posting remotely after visiting with my mom on her birthday) so let's get a conversion in shall we?
Here is a Fire Nymph from the Tome of Horrors now for Old School Essentials. An update to my 5e version.
Nymph, FireArmor Class: 5 [14]
Hit Dice: 2* (9hp)
Attacks: 1 x magic (charm) or burning hands (1d6 damage)
THAC0: 18 [+1]
Movement: 120’ (40’)
Saving Throws: D10 W11 P12 B13 S14 (4)
Morale: 6
Alignment: Neutral
XP: 25
Number Appearing: 1d4 (1d6)
Treasure Type: D
This creature appears as a very attractive and beautiful female with long, flowing fiery-red hair. Her eyes are pale blue and her skin is lightly colored with a cinnamon hint to it.
A fire nymph is a very beautiful creature that dwells on the Plane of Fire. It is akin to the nymph and dryad, though its origins obviously lie elsewhere. Fire nymphs rarely visit the Material Plane, though mages are known to request their company on occasion. A fire nymph is most easily summoned on Midsummer's Eve where they can walk about and interact with mortals and other fey. A fire nymph usually wears translucent robes of white or ash.
Fire nymphs can charm like a their terrestrial cousins, but they can also cast a burning hands spell three times per day. Additionally, they have immunity to fire and take double damage from cold.
Summoning a fire nymph is relatively easy but not without dangers. The nymph's passionate nature causes her to move from one emotional extreme to the next very quickly. When a fire nymph is angry, her hair will burst into flames.
Also, due to their passionate nature, there are many gifted pyromancers that claim to be the offspring of a wizard and a fire nymph.
Fire Nyphs are also known as Pyroeads in some arcane circles.