Extending her life span alters who and what she is.
the character will suffer.
Just like how they took the Doctor out of sickbay with his mobile emitter.
Of Maquis Starfleet tensions evaporated over night.
Or they didn't run out of torpedoes half way through season one.
Seriously, there are author out there that think that Superman should get over that kryptonite thing.
That being said.
Transfer her conciousness like they did with Denora Pel.
Although that's not really immortality, it's just being a bastard to your child.