Hello, In the story I'm working on, there is an incident I'm planning in which my protagonist discovers her father isn't her biological dad. Except I'm stuck on how she should make this discovery. The whole organ/blood donor wouldn't fit, because she doesn't need anything like that, and adding it just for that reason would be unrealistic. What other ways are there? Any suggestions? Thank you in advance!
Finds her birth certificate and somebody else/nobody is listed as father? Is doing a family tree project and finds adoption papers or whatever? Her mother tells her or she finds her mother's diary from the time?
Real father turns up or maybe grandparent tells her or she's having an argument with someone that knows and they blurt it out.
Other options: Her father is ill, she gets tested to donate: blood/kidney/bone marrow and doesn't match. Whether she needs it or not, she could be the donor: She donates blood and finds she has a rare blood type. Her curiosity or casual conversation leads her to find out her father cannot be related. It could be as simple as finding out she has Rh- blood and both parents are Rh+. There are many options around Rh- blood.She finds a letter from her real father. She finds a medical record that reveals it (again, a number of options). Her real father reaches out to contact her. She meets her twin (or a sister that looks so much like her she begins to ask questions).
In House, the MC works out that his real father is in fact a family friend, because of a birthmark they have in common. He then manages to compare his DNA with his father to confirm that he was not related to him. Subsequently, he manages to confirm (via DNA) that his "birth" father isn't either!
If she's in school, maybe she found out because her science class did an experiment to determine their blood type and she did her father's, too, out of curiosity. Or she could have been studying DNA and wondered why she has dark hair when her parents are both blond. (Though, DNA in humans doesn't always work out that simply.)