My 3 and a half year old daughter still isnt potty-trained. what should i do?

Reward socialization: "outsourcing", i.e. Putting up a social construct. "honey, [your best friend's] playgroup wants to have you come, but they don't want to have to deal with dirty diapers". See what you can do about making simple rewards in the social sphere, ones pertinent to her interest.

Visit pediatrician: Make sure you take her to her doctor first to make sure there isn't a cause as to why she isn't potty training yet. If everything checks out ok then the rest is up to her. Having 4 kids myself, i've bought a toy they really wanted and gave them 30minutes of play time with it every time they went and then the toy got put back away until the next time they went.

She'll train herself: Bladder & bowel control maybe the only thing in her life that is completely in her control. Imagine someone always contolled the food u eat, clothes you wear, where u can & cannot go, when to go to bed & who u can & cannot see.U probably give her some lattitude, but u can't control her bladder. Give rewards, but try to ignore if poss. Voiding dynamics are complex, u can't train to relax sphiincter.