I wondered about this when I saw that she looks very much like at least one of my paternal relatives whom's fully Askenazi. When I checked what "Zelnick" means, meanwhile (since I wondered about this, too), I went, "I was right [about Ivana Trump]!" Per Ancestry, "Zelníčk" is Ashkenazi Jewish (Some say that her father's variant was "Zelníček", meanwhile.):
"Jewish (eastern Ashkenazic): occupational name from Yiddish tselnik ‘haberdashery’ or from Polish celnik ‘tax collector’. Americanized spelling of Slovenian Zelnik, a nickname or topographic name from zelje ‘cabbage’."
By the way, other European-language surnames that belong exclusively or almost exclusively to Jews. Such names are Munka (as in my own family, as it is exclusively Jewish in Eastern Europe) and Chesnick (a Croatian-English rendering of"Česnik" (e.g., Sister Cathy's father was a Slovenian-American Jew with Ashkenazi Jewish ties, as Southeastern European Jews are usually Sephardic.).
In Ivana Trump's case, then, she has the right to be considered a Patrilineal Czech Jew. In addition, this helps to shed light on Anti-Semitic Tr**p's brutal treatment against her—now wonder that Ivana disclosed that her husband is a Neo ******, since she as a Jew (if she ever suspected or knew that she is Jewish) to partly explain why she was afraid of her Neo-Nazi ex husband). This also helps explain that D****d Tr**p's children by Ivana Trump ought to be more ashamed of their Anti Semitism, as should be Jared Kushner.
As for Franc, incidentally (since her mother's maiden name was "Francová") :
"French: from a Germanic personal name derived from the ethnic name for a Frank. French: nickname or status name from franc ‘free’ (usually denoting a freed slave). Slovenian and Croatian (northwestern Croatia): from the personal name Franc, Slavic form of German Franz, all from Latin Franciscus (see Francis). Polish, Czech, and Slovak: from the German personal name Franz."