Pilgrim Bellclaire dead (Tombstone/Ressurection?)

I'm a blue knight and yes I have to wear my ring for you to summon me and you must be in human form with your ring on to summon me. I've been summon from random places all across the map, even to areas I hadn't yet been too. The only place I wasn't summon to was the bell tower as that was a pvp area for the protectors of the bell covenant. If you were in that area, if you weren't human, if you weren't wearing the ring and one of us wasn't wearing our ring, that is why you couldn't summon one of us.

As for summoning and invasion The way it worked in dark souls 1 and dark souls 2 are different to make it more fair. It depends both on soul level and soul memory. Your soul level is what level you are while your soul memory is based off of how souls you spent on your armor weapon and levels. You can find it in your player status menu. It's to help fight against over powered people fighting under powered people.

Hope this helps and praise the sun.

As of current knowledge the best and most efficient way of making tombstones appear is by Quit/Reloading until they appear. I have in personal experience had NPC's come back anywhere from the first reload (immediately after killing) to the fourth (also immediately after killing). Also be aware that the Tombstone locations do not completely correspond to the locations you killed them, and you may have to search around to all locations the NPC goes to.