It wasn't that she didn't want to believe Eric's soothing and pleasing words, it's just that to her it was impossible.
While Eric could have his great stealth ability and might even escape under the pursuit of a Realm 5 Master, he was still unable to deal with a whole family of them.
Her Li Family already had quite a few Realm 5 and even some Realm 6 Ancestors in their midst. The Cui Family was a bigger fish in the sea than their Li Family.
The foundation and structure of the Cui Family were something that even her Li Family didn't dare to take lightly.
So, even if Eric had the wish and desire to block the falling Heaven for her, he would still be unable to, just as he was unable to win against the Cui Family.
Of course, there was the possibility of her running away with him from the family, but that was something she could never do.