[Spoiler] Why Li Su Su is hell-bent on saving Xiao Lin, from a novel perspective.

In the novel it was revealed to Li Su Su before she traveled back to the past by her Master that this life of Xiao Lin is the final trial on whether he can be immortalized to become Gongye or not. The Gongye we saw in episode 1 was a human that cultivated to become immortal. If he fail to pass his test to become immortal, he can never come back again as the Gongye we saw in episode 1. Li Susu doesn’t know how or what those trials are. She doesn’t want to risk it and just want Xiao Lin to live so that he can complete his task to become immortal. Because she believe that if he dies now, there will no longer be Gongye, her senior brother 500 years later, even if she does end up killing the Devil God. It was never explained in the drama (yet) about the importance of this life for Xiao Lin. Don’t know whether they are planning to but hopefully they will give us an explanation in the later episodes. 

 Linger:

Good of you to share the reasons. Unfortunate that the drama version has not reveal this yet, possibly cos of the number of episode constraints?

Don’t really know if they are planning to touch base on it. It really depends on how the editor/director want to deviate from the drama. Maybe they thought it wasn’t too important and use it as a wedge between TTJ and LSS. 

XL is a nice guy so LSS will always want to save him.

"hell bent" is right.  WTF was she thinking? She has no clue what his trial was.  It could very well be a noble death which she is preventing him from. But he's definitely destined to die in this lifetime since they have different names.  She's endangering her whole mission to save the three worlds or however many peoples and lands future TTJ is supposed to have destroyed. 

PS. thank you for sharing her rationale

In OG. There no plot LSS saving XL cz there not plot XL imprisoned by TTJ. LSS controlled to kill XL when she runaway from TTJ and on the way back to Sheng capital with YBC ( Chapter 54)