After the creepy way she tracked the other woman down, the lies she
told to gain trust, now she wishes to re-appear, with another, new, even
more fanciful story trying to gain entry and her evidence is: She CLAIMS she has different
blood type than her parents.
This woman is nutso. DO NOT let her into your house, much less your family.
If she is so sure, let her contact an attorney, and pay for DNA testing all around. Then, IF she has more solid proof, she can go forward.
Otherwise, dream up a different illusion and leave that family alone.