Just had a thought - what if, in the Death Star fight, the clip of Leia dying is shuffled forward slightly, and spliced in as Rey is healing Kylo. Then the implication would be that Leia sacrifices herself, allowing Rey to channel her life force into her son? That also explains how Rey is able to heal a mortal wound without killing herself, like Ben did when he healed her.
Except Ben and Rey had most of their life force drained by Palpatine; Ben used the rest of his that Palpatine didn’t take to resurrect the deceased Rey.