There are many well written strong girls in PK dramas but, since we are talking about unmarried ones, I can only think of few.
From the top of my head, Kashaf who I feel is a brilliantly written character. Her determination to do something in her life, to earn a living, a name, to give her mother a good life is admirable. Futher she doesn't aspire to win the moon or anything unattainable, she just wishes to be independent enough to make her own decisions. She struggles through life yet doesn't give her up her courage, doesn't give to worldly charms (even though she is lured enough in college) and stands by her principles. She is the strength of her mother and sisters yet has flaws of her own making her more relatable.
I can go on and on about her, watching ZGH the times I have, i can probably write a thesis on her đ So I'm just gonna stop.
Next, Meera (Urwa Hocane) from Udaari was a pretty strong character too. Even though she despises her family profession and keeps sharing that loudly, she stands by her family and her mother when needed. Further she doesn't get hung up on a guy who insulted her, in fact tries her best to move on from him and make a living. She is hardworking and does her best to improve her singing and slowly adapts to the ways of the city without giving up her true essence and identity and she does it to develop her career. Even later on when Farhan's character proposes to her, she doesn't accept (even though she likes him) cause his mother doesn't respect Meera and her family. She also changes the financial status of her family, educates her brother and helps her neighbour (Sajeeda and Zebo). Lastly, she does get harassed two times, yet fights both the times and doesn't let those two incidents affect her in anyway.
Third, I would like to say Ajiya Ali (Iqra Aziz) from Suno Chanda. Even though she does inappropriate things and sometimes gets on the nerves, she is very passionate about her studies. Also she doesn't compromise on anything that she feels is wrong and is very vocal about her choices. She doesn't give up her dreams and stands by her decision to get a higher education and earn a living.