There are just hints about rogue/warrior way to kill her, but anyone has achieved it as cleric? I am just curious because it's one of the few quest I didn't have done yet and it would be nice to know if it's possible.
Yes, the Cleric class has killed the Unweakened Undermother. While the Cleric class has the least ability to address the stun effect issue, the Cleric skill Intervention helps the class stay alive in the fight. Clerics can also automatically use Restoration Scrolls which are very useful in the fight.
People have killed the Unweakened Undermother with every class at every level of difficulty. Most (if not all) builds have killed her too. With the archer-trap fixed, Archer Rogues have a little more trouble but very doable.
If you have STUN IMMUNITY, than the worst part of the Undermother is addressed (her stun attack) but she does have a lot of hit points and does some serious damage so bringing a lot of top tier healing potions will help.
With Restoration scrolls (they bring Companions back from the dead), I'd suggest using Grissenda as she has better defense and attack. However, since you don't have Magical Training, it might be better to use Hirge with a healing build. Epic Omelettes plus Hirge is a power combo (Epic Omelettes restore half of your HP/MP, but since the last update, can they be used in a fight?, I forgetting now).
Don't forget your Companion can use a potion or scroll every 3 seconds and so can you so every 3 seconds, you should be downing 2 potions. Health is good, obvious but defense and attack potions help too.
You can bring a hired companion and a summoned creature into the fight, they might not last too long but it can help spread out the early damage.
As a 1-handed warrior, you might want to go head to head with the Undermother, you'll take most the damage but that will allow your companion to last longer. You can always pop out for a second to heal if needed but don't let your Companion die.
equip full gear set with spirit resistance and use 2 handed weapon with flurry and bring the campanion that can heal you and let her wait without attacking just healing you....make sure u have lots of hightest tier of HP pots with you
I just beat her with my mage lvl 21. If you have a magic character or companion i highly suggest the golden apple potions. Weapon wise anything non elemental or spirit based helps she is immune to fire ice lightning etc. High spirit resistance helps too so she doesnt stun you every few seconds. Potions of galade are a huge help it boosts your armor while healing you. Its a long fight i also ran behind her and dropped my 18 lvl iron golem to flank punch her in the butt. I fought her with the cleric companion Hirge.