A medusa is a Monstrous Humanoid and only Humanoids who die of ghoul fever rise as a ghouls. But in any case one "who becomes a ghoul in this way retains none of the abilities it possessed in life".
For simple fear-effect, I found that a Mhorg can create Zombie-spawn of "creatures." Vampire can also be added to the Medusa template (humanoid or monst.humanoid).
I'm picturing a Vampiric Medusa riding a Zombie Unicorn... Ahh, a combo for my next RPGA submission CR7+2, + CR2 = CR9 encounter. Not hard, but should be enough to get the goats up on a few good elvish characters
SRD:
A character with negative levels at least equal to her current level, or drained below 1st level, is instantly slain. Depending on the creature that killed her, she may rise the next night as a monster of that kind. If not, she rises as a wight