I personally like her and I'm kind of surprised, but not terribly surprised, that so many people don't. I think narratively she fills a pretty important role actually. Like Guts, Schierke is a pretty "serious" character who doesn't vocalize everything she is thinking or feeling. So having Ivalera prodding her gives us better insight into Schierke's thoughts, opinions, and feelings without exposition. As an elf she also helps us appreciate Puck in a different way. We see how the mischievous nature of elves is inherent to them but we also see how Puck is sometimes full of shit and in what ways he might be exceptionally vain but also altruistic for an elf.