Okay, I'm back.
Brainiac 8 said:
The goal of isobel was that she was to destroy the teague line, because of what they did to her...but when Lana stabbed Dr. Quinn; Isobel left Lana's body. What doesn't make sense is that Isobel failed her mission as far as she would be concerned, because she would have thought that Jason was still alive. Thus her mission wasn't complete, and as far as she would know, the Teague line still lives. Jason was dead at that point, but Isobel didn't know that.
Here's a line from the transcript, just before she is set aflame.
Isobel: You think this ends with a lick of flame? I sleep but a while. And when the time is appointed, my heir will awaken me and I will have vengeance!
She said she would have vengeance. She never said that she was going to destroy all of Gertrude's heirs. She got her vengeance by killing Genevieve. Jason was nothing without his mother, thus her vengeance was made and Isobel left.
Next, Isobel took over Lana, and she used the book to bring back her two witch buddies also, and they possessed Chloe and Lois. When Clark burned the book, the witches left their bodies, or so it seemed. But we find out that Isobel was just hiding in Lana's body, and would resurface when needing too. Why wasn't that the case with her two witch buddies?
Wouldn't Chloe and Lois still be harboring the other two witches also?
The spell Isobel used to bring back Briana and Madeline was a potion spell, obviously not as powerful as the spell that Isobel used to resurrect herself in one of her decendants. When the book was destroyed the spell was broken, much like the spell that Isobel cast on Lex. When Clark pushed the piano away the spell was broken.
However, the spell that Isobel used on Lana was cast in blood making it more potent.
I can kind of fanwank that one.
Third, Isobel would resurface when Lana was in danger or in pain, such as in "Sacred." But Lana was constantly in danger, getting beat up or something throughout season four. Since Isobel obviously wanted to preserve the bodies life that she was using, why didn't she resurface more during other dangerous/painful situations?
Okay, lets got through each of the episodes since Spell and see how much danger Lana was actually in.
5.09 - Bound
This episode was a Lexcentric episode, Lana met Genevieve for the first time and was barely in the episode so she wasnt in any danger at all.
5.10 - Scared
Lana was exposed to a psychological toxin which would probably mean that Isobel was powerless.
5.11 - Unsafe
I guess if things had gone too far Isobel could have saved Lana from having sex with Jason, but fortunately it didnt get to that point.
5.12 - Pariah
Jason was able to save Lana before her life was in question.
5.13 - Recruit
I guess Isobel could have saved the audience from listening to another one of Lana's speeches about lies and secrets.
5.14 - Krypto
Lana was only seen with Chloe in this episode. No threat.
5.15 - Sacred
Isobel makes her second appearance.
5.16 - Lucy
I think everyone should have been worried about saving themselves from Lana in this episode. This is the episode when we got to see that Lana can also play the game that everyone does on her.
5.17 - Onyx
Lex kissing her was the only real threat. She stood her ground and sort Clark out for help in this one.
5.18 - Spirit
Another psychological disorder that most likely rendered Isobel helpless. Must have been squeezy inside Lana's body in that episode.
5.19 - Blank
No threats in this episode. Just some lovey dovey eyes from Clark.
5.20 - Ageless
Exploding babies. Me say no more.
5.21 - Forever
She was frozen or whatever it was that happened to her, so her body was disabled. Isobel wouldnt have been able to present herself.
5.22 - Commencement
Isobel made her appearance when Genevieve was choking Lana.
There you go Avid, three major plotholes of the witch/stone arc.
There ya go, 3 answers.