Definitely spend some humanity to reverse your hollowing if you haven't already Magus, increases your health, gives you more survivability, even without summoning. As I said before and the others have said as well, summoning Mildred is probably a good idea - in my experience she doesn't always survive that long, I've seen her just stand in the lava before, but it should be long enough to deal very decent amounts of damage - so reverse at the fire, kill the invader and then try again.
I fired up my Dark Souls 1 earlier today, lo and behold I had a save not to far before fighting Queelag, took me a few tries to get into the swing of things, so rusty.
Refreshed my memory though so some info on her attacks. The lava pounce attack is only used at distance, as such it's best to stay close - if you're right up next to her on her left side you can actually completely avoid the flame sword attacks without dodging or blocking, just run into her - however, she'll usually use the AoE attack if you're close and attacking after her sword combo finishes, keep an eye out for it - she slumps over the spider's head - and run whenever it looks like that's about to happen, circling round to get close again and avoid her using the pounce - don't lock on during this. With Mildred you can simply let her take the brunt of the attacks and always try to attack from behind while Mildred is still alive. In this case you just have to worry about her spinning around and spewing lava in your direction, or the lava spit attack which is always followed by her leaping to reposition herself, keep and eye out and try to keep Mildred between you and her. If you attack from the sides though she can stomp you so try your best to be behind her while Mildred is distracting her. If you're forced to fight in front of her I think she can be stunlocked if you have a weapon that can actually hit her body as opposed to the spider, the overhead on the Halberd might be able to do this, I didn't try this tbh, but if you're creative with your stamina usage there's no reason she couldn't be perma-locked.
This post has been edited by WinterPhoenix: 25 February 2017 - 03:23 PM