I'm-- ["not afraid of you" is what she was going to say, which would be mostly true if with a hint of bravado, but... it hits her that it's for the best if Yuuki believes it's her Elsa's afraid of.
There's a pause, which might seem like she's struggling to believe Yuuki's words, but really she's trying to figure out how to ask and make it seem like concern for her own safety. Eventually she settles on:]
Vampires are... strong, resilient; inhumanly so, yes? They don't succumb as easily to cold or- [deliberately misleading example incoming] hunger, or anything of the sort. [...] I-it should be fine as long as it's quick.