This chapter's just for explaining the last one so you can skip it if you want.

Lee's death affected Clementine greatly, since he practically raised her and taught her how to survive. In the moment she ended up in, he was already bitten. So she could let him turn or shoot him again. Lee got bit while looking for Clementine after she ran away to find her parents. Even little Clem thought that was her fault (season 2 when she meets Kenny). Which is why I made her act and think like this. I don't really agree with what Clem is telling herself but she isn't exactly in her right mind during these moments. But looking back to 4am this morning (when my thoughts are most rational) I think I made Clem not want to change the past because

1. Lee was already bit

2. If she hadn't run away, and Lee was still alive then she wouldn't have met Rebecca and the others and most importantly—AJ.

She loved Lee and clearly would've wanted to keep him alive. But if she did, she wouldn't have met all those people. If Lee was alive, she would've still gone with Christa and Omid. Since Lee was there, Omid might've not died and they wouldn't have been overwhelmed by those bandits who killed Christa and caused Clementine to fall into the river. That meant that she wouldn't have met Rebecca and Co. (the group had no particular leader and Rebecca was AJ mom so just stick with me)

Anyways, whoever much Clementine wants to keep people she loves alive, she couldn't change anything without altering what would happen to her in the future. She wouldn't have found AJ, Richmond, and Ericson if these were altered. Just a random explanation for you.