Whats wrong with my baby

So, my gf told me this wasn’t there two days ago. But rn the end of her tail is scarring me, is there anything we can do ourselves or should we take her to the vet ?

So, my gf told me this wasn’t there two days ago. But rn the end of her tail is scarring me, is there anything we can do ourselves or should we take her to the vet ?