I do not exactly know, what changes are used - but it looks very strange and very amusing.
First: There seems zo be a little bug in your d5_class.2da script. CVMYSTRA is FIGHTER_CLERIC when I met her at LIONS WAY, you defined her as CLERIC inside d5_class.2da.
2DA V1.0
ALL
CLASS
CVMYSTRA CLERIC
should be
2DA V1.0
ALL
CLASS
CVMYSTRA FIGHTER_CLERIC
when I compare it with a the complete file after installing F&P.
But this seemed to be only one part of the problem.
I inspected SANDRAH in DLTCEP and changed item restrictions. The easy way is to remove all class restrictions. But this will make them usable by everyone with required str, con, wis,,, So I only added the three classic kits (I think I will need NI again even if I don't like it, in DLCTEP I did not find the new kits as an option for items) Selecting cleric-kits makes the armor usable, but for the rings I needed full selection. I think this is no great problem - because you are using a script, that all items will be deleted and restored, when anyone else puts them in his inventory.
Just not more than a brutal workaround and I do not know if these changings will have consequences in the game - but it seems to be a possible solution for the coexistence of SANDRAH and F&P.
And if you would edit the items set there prices to zero. I have quitted my MegaInstallation shortly after I sold SANDRAHS items - now I have manually edited the restrictions for her inventory and opened my safegame - short time after selling everything she wear in the temple in FRIENDLY ARM. I only want to look, if all items are now useable and wander: they are in the store and some of them in her backpack. Running around, all showed up again. A very simple trick for making money without cheating.