i had something like that happen with a sim for cooking she had gone to cooking class the skill didn't appear so i just had her read a skill cooking book the skill kicked in have your sim buy the books,read them see if the skill increases see if that works first for you
I sent her to class and had her read. still nothing.
do you use mods ? they may need updateing to your game patch level
edit to add also try clearing the cache files
delete the cach files go to electronic arts/the sims 3/
•CasPartCache.package
•compositorCache.package
•scriptCache.package •
simCompositorCache.package
•socialCache.package.package
it's safe to delete these files as a new ones will regenerate
