We know Lenneth's talent is to hear the voices of people suffering just before death. The way Freya says it in the game, you'd think this is her talent, specifically, and not a shared skill all three valkyries possess. If you look at it the right way, you can say this talent is involved with the present, in that she's called by her einherjar - so to speak - as they're dying, versus before or after. Perhaps Hrist is drawn by an einherjar's reputation (I'm sure you can interpret that metaphysically - their prowess generates a certain kind of astral mark, or something like that), and accompanies each one for a time while they're alive, and only takes them when she considers them ready.
If the scene re: Hrist's einherjar in Valhalla showed us all of her recruits, then she has significantly fewer than either of her sisters. However, it sounds like she spends more time
Silmeria seems to recruit her einherjar - sometimes - after their deaths (versus by her own hand, or the instant they die), whether they be natural or earned in battle. I was reading a Wikipedia article concerning VP characters (I know, I know, but I don't have time to replay the game to catch the einherjar I missed!), and several of the profiles noted that characters lived well past the periods of their lives I'd consider heroic. Phyress, for instance, died at 58, but it doesn't sound like she died in battle. Seluvia and Christie just disappear; they could have died at any time, of old age, battle wounds, or whatever - if Silmeria allows one einherjar to materialize at a younger age than she actually died (Phyress again), why not others?
That can't always be true, though, as several of her einherjar died in battle, and there's no indication Silmeria waited to pick them up. And then, Hrist recruits a soul that has been dead quite a while. I don't remember why she did that instead of Silmeria.
(Addendum: the difference could be simple in cases like this, where technique overlaps. Silmeria might recruit only after destiny has run its course - that is, without interfering in any way - while it could be Hrist's habit to mess with them even before they die, to mold their experiences to her satisfaction. This could lead to more satisfactory results when she moulds their souls after death.
Silmeria, as representative of the Future, would be all about the potential, the results she could have, and less interested in the past. She's adamantly against interference of any kind, for sure.)
The more I think about this it's silly, but I like the idea that the valkyries are actually influenced by their roles of past, present, and future. You really don't see much of it in the games, otherwise. I've always thought Tri-Ace combined the Norn and the valkyries so they could get away with having only three.