I am pretty sure this is not true. Sorilea may have been the one to know the precise details, but I think the fact that Cadsuane had the DB and CK was common knowledge. It is mentioned that Cadsuane had been testing the female a'dam, and asking permission to test the male one too. We know Rand had been asking for the access key back with Cadsuane refusing to give it.

No, it was no secret that Cadsuane had the DB. The only thing unique about Sorilea is that she knew the exact location, but thats not a big deal since Cadsuane was stupid enough to keep them in her room which would be the first place anyone would look. All Elza would have had to do was enter her room and search for a while to discover the box and the wards. And since Cadsuane was not present and visiting the WO, Elza would have had plenty of time. Sorilea is not required.

Again, according to BS, Elza broke the warding on her own thanks to something SH taught/did to her. We don't know how exactly, but if you search back you will find that its been speculated that she was given temporary access to TP and other possibilities. But again, Sorilea is not required.

Maybe there is, or maybe the Aiel are unique in that they were better at keeping DF away due to their culture. Maybe its Rhuarc. Maybe Amys. Or one of the maidens. I don't deny the possibility that Sorilea is a darkfriend, but at this point it is just speculation, and the DB incident neither proves or disproves it.