Gwynneth joins the Dark Elves as part of the second set of fragment champions earned from the Doom Tower Secret Rooms. Doom Tower Fragment champions cannot be summoned.
On paper, Gwynneth has an interesting kit with some unique abilities. Any champion with an AoE a1 ability instantly makes them viable through Stun artifact set. In addition, not triggering counterattacks makes her valuable into Valkyrie waves or in Doom Tower especially against Agreth.
Her A2 has a potentially strong heal if the damage can produce a big enough number and if Gwynneth is already full HP – but this would be quite situational to activate. Her A3 could potentially do significant damage to heavily debuff targets.
Her viability will likely live and die by her ability to hit hard, with her heal requiring damage.