Her Only Chance
It was unusual for a child to get placed in a new home at 6 years old. At the orphanage, everyone felt like Lise getting adopted so late was likely going to be her last chance. This is probably why a lot of information about Lise’s background was withheld from him when he chose Lise.
They were worried that knowing more about Lise’s background would make him change his mind. Eventually, they were confident that Dale would come to know the details about Lise’s past, but until then, they were happy to keep it all secret if it meant Lise would be successfully adopted.