Unknown Grandfather may save my mum

[YasminCarter]

Hello All,
I am hoping someone here might be able to help me or point me in the right direction. I am a kiwi living in the US. My mother is here with me on a humanitarian visa (health issues). That visa is now being rejected due to a change in policy from the Trump government. My only hope of getting her to stay is if I am a citizen. That’s where you come in. My dad was born in Sydney, Australia (1955) to an unknown father (Mother was Ellen Margaret Keough) but rumor has it he is American. I took a DNA test and there are definitely some links but I just don’t understand how to figure out all the links etc.
Can someone help me?
Thanks,
Yasmin