In the book "The Face on the Milk Carton" by Caroline B. Cooney, Janie's birth name is Jennie Marie Spring and her adopted name is Janie Elizabeth Johnson.
Jennifer's full name is Jennifer Marguerite Sands.
This movie is set in North Carolina with both families living there; Wilmington (Jessamons) and Carlington (Sands). In the books the Johnsons (here Jessamons) live in Connecticut whereas the Springs (here Sands) live in New Jersey.
In the book the biological mother is not called Sada Sands, but Donna Spring. The the biological father's name is the same; Jonathan.
In the books Janie/Jennie has 4 siblings, Stephen and Jodie, as well as twins Brendan and Brian.