Why don't you tell us more about Ursula. Where did she migrate to and the marry Anton in the US. What is her full birthday and date of death. What are Anton's birth and death dates. Who was Ursula coming to the US to be with?
You can join my Facebook Genealogy group where we have all kinds of expertise (many from Slovenia) doing Slovenian research. https://www.facebook.com/groups/183735961660531/
What is your mom's destination in Slovenia.
I looked and I have a Margaret Stubler married Mihael Sustersic in Novo Mesto.
You can also contact me personally at firstname.lastname@example.org
and I will see if I can help you out.