she doesn't commit suicide
the lady of shalott doesn't commit suicide
she lives on shalott
she is cursed and cannot see the world directly(because of the curse) which means she can't just go up to people and talk to them or see them like face to face
then she hears sir lancelot singing and falls in love with his voice
she goes to see him (wether or not of the curse she doesn't really care of it! as a matter of fact she doesn't know she is cursed!!)
she gets into the boat and tries to see sir lancelot but she dies on the way there because it's so cold(it says in the poem that her blood freezes and her eyes turn black). the boat keeps going down the river to camelot and when it arrives everyone gathers around her. they look at her suprised and wondering why she is dead. then sir Lancelot looks at her and thinks she is really pretty.
but if you couldn't understand me here is the short version:
the lady of shallot live on shalott henceforth "the lady of shalott".
she is cursed and can't see people directly.
she hears sir LAL(lancelot) singing and fall in love with him!
she goes to see him in camelot by riding down the river by herself in a boat but she dies on the way there because she is cold(she freezes to death). (you'll see in the poem it doesn't say anything about guinevere)
then her body keeps going down the river in the boat intil it reaches the shore of camelot. sir lancelot thinks she is pretty.
THE END! hope i helped!!