Could we just have it so she only explains to BB-8? Something like “I learned that from the ancient texts. Transfered life force from me to him. You would’ve done the same.” I mentioned earlier how it doesn’t make much sense Rey would feel the need to explain to Poe and Finn, who don’t show much interest in her training, specially since they’re supposed to be in a tense situation (and also I don’t like adding lines the second the mouth leaves the frame, it’s the same reason the Leia lines don’t work for me).
But BB-8 does show interest in her training, he follows Rey around while she trains, and he beeps something about trying to help when she says she’ll earn Luke’s saber one day. We already have him asking Rey what she did so here’s where it makes the most sense to add that exposition. I prefer this power coming from the ancient texts because they were a big deal in TLJ but here they’re never mentioned, other than the scribbles about Exegol Luke apparently put on top of them.
As for Ben being able to do it, I always imagined it’s a result from being a dyad with Rey, “two that are one”, as well as already seeing her execute that power on him. Palpatine also executes an “evil” version of this power by absorbing life force instead of giving it, which makes sense since the Sith spirits would date back to “ancient” times as well.