First off there is never a change in the shape of a shell-nucleated pearl. Shells stay the same shape they came in or were shaped into balls and they stay that way. I sincerely doubt the nacre changes either, except from an outside mechanical action- or we have would have heard about it.
I got out an akoya pearl choker that once belonged to my MiL.It was from Gumps in SF. It is a baroque strand with the larger more round pearls in the front. Then the sides have several barrel shaped pearls, even one skinny dropped shape. There is no sign of wear around the thread or on the surface-though they have lost a lot of luster. I tried to get a photo but my camera lost its charge and I can't find the charger. I'll keep trying.
So, my best guess is that your strand of pearls came that shape and stayed that shape.
(Did your appraiser take the GIA Pearls (or equivalent) course? If not, it is possible that she, like thousands of jewelers, doesn't know much about pearls except recognizing them and having a rough idea of what the current market value is. (Baroques are usually valued less than rounds).