IIRC Jadwiga (Władysław's daughter) was proclaimed as heir to the Polish crown IOTL, before her brothers (Władysław III and Casimir) were born. It is very possible that the same thing would have happened with Elizabeth. But I agree that the Polish noblemen would want the king to remarry in hope to have a male heir(s).
The political situation of Poland (and Lithuania) when there is time to talk about Elizabeth's marriage would be interesting. In 1409 the war against the Teutonic Order started; Poles need allies. Where would they look for them?
I think Bogusław IX (young duke of Pomerania Stolp) would be an interesting possibility. IOTL he was considered a potential candidate for Jadwiga's hand. In 1409 he would be 4, so 6 years younger than Elizabeth. OTOH Frederic of Branenburg was another candidate as husband for Jadwiga IOTL when he was 5 years younger than her).
Anyway, IOTL Bogusław VIII (father of Bogusław IX) was considered Poland's important, but not exactly trustworthy ally against the Order - he switched sides a few times, eventually fought on Polish side in the battle of Grunwald in 1410. An offer of marriage for his son with Polish princess might be a way to cement his allegiance to Poland. True, she would have to wait with marriage until she would be about 20, but theoretically it would be possible. Besides, a betrothal is not a marriage yet.
So let's imagine, that other things happened as IOTL - Poles and Lithuanian won the war. King Władysław remarried to have sons and Jadwiga's betrothal was still valid. And then in 1418 Bogusław VIII dies. IOTL Bogusław IV was too young to rule, so his mother became his regent. But WI king Władysław saw an opportunity and offered himself and/or his rappresentative as regent until his future son in law can rule himself. His motives are not only political - he honestly wants to ensure a good future for his daughter. His position is not bad: his daughter is to be young duke's wife and Bogusław VIII was officially Polish vassal. There is also a carrot - if Władysław has no sons, Bogusław's children (or Bogusław himself) will have a claim for Polish throne, as it was IOTL.
After Bogusław is old enough, he marries Elizabeth and fully cooperates with Poland against the Order. Now, if Władysław II has sons as IOTL that would end only with strongly pro-Polish duchy in Pomerania, more or less as IOTL; if not, well - we might have a Griffin dynasty on Polish throne, union of Poland and Pomerania (well, not whole Pomerania), earlier Polish foothold on the Baltic Sea and IMO more west oriented Poland, since born and raised in maritime country Bogusław IX (or king Bogusław I) would be less interested with Lithuania and eastern expansion, especially with not so strong claims to Lithuanian throne.