Ok - I went human in the depths and had this NPC AI invade my world. I managed to kill her so then I could summon her before I faced Queelag (who is not anatomically correct I might add). Anyhow...... in the entrance to Queelag's den I saw another summons mark, so I summoned the player and ran down to the foggy entrance to summon Mildred. I ignored the egg-type blobs coz I heard they can be a nasty pain in the asp.
But it looked like the player I summoned before couldn't join so I went back to the top of the cave entrance to see if I could try again, Mildred followed me and started attacking the egg-type things that are there!! THEY KILLED HER. I actually laughed. So I ran back past them to the entrance and thankfully found another summons mark for yet another player. This time the summons worked and we kicked that fire spitting lady's spiky ****.
Hint: don't let Mildred wander!