Apparently, it was required to be allowed in that state:

Reading a bit more, during the sentencing phase in that state people making victim impact statements can choose their format for expression, and it's entirely allowed to make statements about what other people would say. So the judge didn't actually have grounds to deny it.
No jury during that phase, so it's just the judge listening to free form requests in both directions.

It's gross, but the rules very much allow the sister to make a statement about what she believes her brother would have wanted to say, in whatever format she wanted.

From: https://sh.itjust.works/comment/18471175

influence the sentence

From what I've seen, to be fair, judges' decisions have varied wildly regardless, sadly, and sentences should be more standardized. I wonder what it would've been otherwise.