Idk. It makes sense for the world ending, sure, but it doesn't make sense if we account for the 'ready' and 'cannot be delayed' part. As far as we know and from what Chao told us, mom didn't want to interact with grandpa in any way, and made Chao promise to never accept the offer to fix his soul in return for the MC. Why torture your husband whom you love with that just to give the MC the option later anyway?
In my opinion it's:
a.) Some crucial information that will help or power up the MC somehow, but that's also somehow extremely worldview-breaking or dangerous. (Hence the 'ready' and 'can't be put off' part. So it has to be something that she wanted the MC to know or get, but not before he was grown and mature. I just can't see it being contact with grandpa after what she made Chao promise and after she literally dropped everything just to get away from him. This is the most likely option in my opinion.
b.) Some artifact, manual, or map towards something of the sort. Now it's a small coffer so it's unlikely to be a weapon or anything directly usable for combat, but what it can be is indeed a manual or perhaps something that was supposed to be the MCs Tang Wei care package, and that she stole from grandpa before escaping. Since she was afraid of him and hated him that much, she might've thought that it would be the only chance the MC would have to avoid going to him, even if she didn't like Tang Wei either.
c.) Any other combination of A and B. A letter from her saying something emotional and then pointing towards something, some piece of knowledge that might get us something, or a letter coupled with a substantial item could be possible.
d.) Another troll reveal from Niki that says something like "I love you with all my heart son, but you're not Tang Ruo's competition. Just become his loyal servant and defeat grandpa and then lick his boots as thanks."
