I am going speak her of her role in Valkyrie Profile 2 : Silmeria, where she is an important character. What I am going to write is really very summarized, I'll write more in depths in a next update.
The story of first part of main plot is not focused on her. It is mainly around Silmeria, the gods and etc etc, but that is not the subject. The story happens hundreds years before VP1, and makes the light on things like Arngrim past life who was an Einherjar of Hrist. But what is interesting in final main plot and Lenneth's part is the presence of a charcater that we could have thought was a previous incarnation from a Valkyrie Profile 1 character here : Lezard.
Like we all know in VP1 Lezard loves Lenneth. But, he couldn't get her, so what did he do? He travelled in time and went in past, at VP2's time, and won power. With the event changed, the world of Lnneth begun to crumble, and she comes in the past stop Lezard.
That is what he expected she'd do. Once she is in the world he created he use the sovereign rite on the Valkyrie and keeps Lenneth in a crystal, wanting to merge his soul with hers. He reveals to be VP2 vilain.
Of Course, Lezard failed since the 3 Valkyrie soul merges at the end, and he dies with his soul condamned to not reborn. But we know that Lenneth reborn and a new futur awaits her from last text of the game. But an alternate ending exist where Lezard reborn too. Poor Lenneth has not finished to be his obsession, except if she finishes by really love him in a new futur and that it be great love ^_^
