Bella had her first heat cycle. Hers were swollen for a very long time.
Her skin also turned a little darker around them? I was very concerned & the Vet said she was probably going through a false pregnancy. The Vet also had me worried because he said that sometimes they will remain larger with each heat cycle.
But, thankfully that was not the case. She was spayed afterwards and is now back to normal.
Good Luck with your little girl!!