Very few people ever pull off anything even close to immortality, and Asmodia is aware that she's not that good at math, to research something that very few wizards have ever figured out. A lot of people want immortality. Very few people get it.
Then again - the other form of the thing she wants - isn't something that a lot of people want. Maybe it's genuinely easier to figure out what the Starstone does to the people it eats, than to figure out immortality. Though you'd think, if it was easy to solve, that Galt would use that instead of their famous soul-trapping executioner's blade, which Asmodia isn't interested in because the Hellknights will get to it sooner or later.
"I suppose a slave's-bread version of that would be finding enough spells that destroy memories and rewrite personality that the person who goes to Hell isn't effectively me any more," Asmodia says, and feels a flare of awful hope as she does. "Reprogramming her to be a faithful Sarenrae worshipper might be funny, she'd be so surprised when she ends up in Hell." Because fuck Sarenrae, that's why.