As K2QC said, they only had to use the drops temporarily and then were able to taper off and stop. These might break the cycle that Sheba is in; maybe she needs a little temporary extra help to settle in by being calmed down enough to see that everything is ok.

HUGS and good luck!

(PS - my vet told me a few months ago that Feliway's patent is over, so it's half the price it was. Rather than use plugins, I got a super-stretchy collar for my cat (one that will just fly off if it catches on something or he and his buddy are playfighting), and put one shot of Feliway into the collar every day. That way, the stuff is right at the source! )