Keira had actually secretly done a DNA test on Howard and Amy after realizing Howard's shady behavior. Back then, though, the results came back showing they were indeed father and daughter.
It wasn't until later, after Ellis's diagnosis with infertility, that Keira understood that people could tamper with medical reports. She eventually found out it was Erin who was behind it. With Erin's influence in the medical world, it wasn't so surprising.
So when she heard today that Amy's biological father was knocking at their door, she couldn't shake the feeling that it might be true and had someone immediately conduct a new DNA test.
To her surprise, the results showed that not only was Sean Church not Amy's father, but Howard wasn't either.
Amy had always resembled both Keira and her sister, Keera; it was obvious to anyone that Amy was Keera's child. Yet now, it seemed like her biological father's identity had become a mystery.