If memory serves, Lifegiving specifically states that it heals no damage, it just puts the soul back in the body. If the body won't support life, they'll just die all over again.
So my take would be either that yes, they'd have to do Lifekeeping over and over until they can heal the damage, or let her die, heal the damage, and do Lifegiving.
Keep in mind that if you let her die, the corpse degrades unless you do Preservation. As Terry Pratchett says, it gets "manky."