Mystery half sibling?

I received my results today and I didn’t expect for all of my “close family members” to be people I had never heard of or met before. They are linked to my paternal DNA as well. One person who sticks out the most is a woman listed between the age of 18–29 (I’m 25F) and we share 30% of our DNA (2121 cM across 40 segments). I’ve done the calculators, I’ve read a bunch of other posts, and it’s still inconclusive to me whether it could be that this woman is my half sister. I want to be somewhat sure that this is a possibility before I ask my father if this could be a sibling that nobody knows about.