I always use my Human Effigy whenever I'm near the boss fog. so I never saw her sign near the elevator.
Anyway. I summoned her three times and she's literally the ret**est Souls series NPC I have ever summoned. so I ran out of Human Effigies and in my 13th time I was able to put this Lost Sinner f****er down without her help.
What I found strange is that no one seems to put summon signs near The Lost Sinner and it seems that a good number of people can't fight him, I placed my summon sign and got summoned in less than 2 seconds there. --- i7 4770K | Asus Maximus VI Formula | G.Skill Trident X 16GB DDR3 | EVGA GeForce GTX 780 Ti | Samsung 840 EVO 500GB | Seagate Barracuda 2TB | NZXT 750w