No one knows for sure, since her ceremony wasn't narrated. But, I would guess the 9 cats were:
- Bluestar (mother) - Oakheart (father) - Stonefur (brother) - Mosskit (sister) - Crookedstar (uncle) - Silverstream (cousin and best friend) - Graypool (adopted mother) - Feathertail (cousin and former apprentice) - Leopardstar (previous RiverClan leader)
I also think Lilystream, Moonflower, Stormtail, and Snowfur would have been there to witness her receiving her 9 lives, but not actually give her any since she hadn't known them in life. The above were cats that she loved and/or were closer to.
Her being accepted by StarClan also proves that Oakheart had been right in what he said while meeting with Bluestar in secret during Bluestar's Prophecy -- StarClan blessed a product of their union.