Remember that she's the one who raised the issue by stating that she was a lesbian, thereby making it the state's business. If someone went in and stated they were a drug user, it would be appropriate for the state to determine if illegal drugs were being used. It would also be appropriate for the state to refuse to place an innocent into the home of the drug user until that was known.
And since the law applies equally to heterosexuals, regardless of marital status, don't you think all applicants for adoption should undergo extensive investigation to determine whether their marriage beds are the site of this "crime against nature"?
Only if the couple first did something to suggest that such crimes were a common aspect of their household, as the woman did by admitting she was a sexual deviant.
Where is proof that this woman has broken the law?
She has declared her intent. To supply the proof that you suggest, the state would have to put her and her home under 24-hour surveillance. Better to just keep the innocent child out of her control.