Okay, but the point of the scene isn't that "Susie dumb". She clearly recognizes it and just refuses to acknowledge it because she has practically nothing right now without her adventures with Kris.

• Her household is extremely abusive and neglectful.
• She's been expelled from schools and clearly has a trash academic record.
• She finally connected with Noelle through her adventures with Kris, and that relationship is just barely beginning.
• Kris and Ralsei were her first real friends and easily still her closest.
• Toriel seems to be the first adult (or even person) who showed her genuine compassion.
• She now literally lives in castle town.
• In her mind, she isn't the hero and stands no chance against the Knight without Kris – who she thinks is the hero of the prophecy – and Ralsei.
• Kris has been, overall, treating her well from her perspective, especially in the light world.
• She's happy for the first time in basically her entire life.

Given she still doesn't really know how dark world stuff works, it's 100% understandable that Kris being (directly or otherwise) the source of basically everything good in her life right now (in a way that's clearly not stable) would get her to chalk it up to circumstance.