i think this whole situation is confusing for naomi, you are not a partner to her mum, so in her eyes perhaps not the "supportive person " of her mother, but JUST a friend..............so you are fair game, she can use you to take our the anger she feels at the situation ie mum not with dad.......................................
claire doesnt want to support you against naomi, cos again you are ONLY a friend........................
you had an opportunity to be able to influence the family dynamics but as you say " our relationship did not really work out, but we remained close friends " therefore you are ONLY a close friend, nothing more nothing less...................................
dont over step the mark, naomi was there before you and will clearly be there when you have gone