The girl I'm thinking of is Isabelle." : La fille ________ je pense est Isabelle. Why is the answer "à qui" rather than "de qui/dont"

I've been meaning to ask but please let me know if Lawless French or KwizIQ has a lesson that lists many of the verbs that require à?  It is not always obvious to me as a student.  Many thanks.

here's a good list that i've found

https://www.lawlessfrench.com/grammar/verbs-with-prepositions/

when you say "think about sb" in french, it is "penser à qn"

hence why it is a qui, not de qui