Morningcalm
Keeper of Records
It's hard to explain, to be honest. Short answer, it feels wrong. Yes, because of her marriage with Jagiello there was union with Lithuania. She was also very pious and generous, she founded Jaggielonnian University (not sure of its name in English).
But she was also very young. Also... tbh, it's not like she had any power in country. Unless some historian can correct me.
And I feel like there are simply better choices, like mentioned Jagiello, Jan III Sobieski, damn, even Józef Piłsudski, even if he would be controversial as well.
Ah, I see. Wikipedia notes she was mostly involved in Polish cultural and political life, but she did the following as well:
In 1387, she led two successful military expeditions to Red Ruthenia, recovered lands her father Louis I of Hungary had transferred from Poland to Hungary, and secured the homage of Petru I, Voivode of Moldavia. In 1390, she also personally opened negotiations with the Teutonic Order. Most political responsibilities, however, fell to Jagiello, with Jadwiga attending to the cultural and charitable activities for which she is still revered.