Bless her heart. I'm
sure that could not have happened 3 weeks ago without you noticing. She must have gotten it caught on something. I hate that she's gonna lose that part of the ear. When you said tip, I thought tiny, but those pics show a fairly large area from what I can see.
That is another reason you could not have missed it if it happened 3 weeks ago. Tissue without blood flow dies quickly. It could have happened as recently as 12-24 hours, although the edges do look like it might be a couple of days. Keep us updated on how she does! Wishes for a quick recovery from that and the dental.