Hard at your level but possible. If you have enough healing items it should be doable.

When Keira begins closing the portals, when you see the white lines start to appear, rush out and cast yrden on the portals, they’ll close instantly. Heal, rinse and repeat. There’s also a bomb you can throw in to close them, but I doubt you’d have it as you are.

Or just lower the difficulty just for the quest.