@Bayaya at the bakery I worked at as a kid, half the senior workers had the tips of their fingers or more missing from accidents with the machinery.
The ones that lost flesh right down to the bone got a bit of a stumpy flat layer of skin grow back over it that looks obviously off compared to normal fingers, but surprisingly better than I expected it to.
Obviously they ain't regrowing any bones.
Her injury looks different to those though, kinda more like they reattached her finger - or her mother screwed up and only half cut it off - and it healed back crooked sort of? I dunno. I've pre-ordered the novel that is meant to come out in about 12hrs (J-Nov premium) and this is one of the things I hope there's more detail covered seeing as the manga really doesn't make it clear - what she's saying and the pics don't match, unless this world has supernatural shit going on?
Edit:
@KABA ah, I totally missed the tip of the finger back then. So she does just have the tip flat thing like the bakers I know have then? I guess the healed fingertip would be more sensitive being thinner, so she probs holds it all gump like that to avoid it hurting like shit - like as a kid it was ingrained in her that it hurt so now she's grown up subconsciously holding the finger away from danger all crooked making it look like a bigger injury than it really is?