I have checked up the early Polish terms
for Venus. The most common one (translating Latin Venus, stella matutina,
Lucifer, Phosphorus, etc.) seems to have been <jutrzenka> (also
<justrzenka>), still used as a literary word for "the morning star" or
"dawn, daybreak". What's interesting about it is its very close relationship to
Lith. Aus^rine., since ju(s)trzenka < *justrIn- < *aus-r-in-. Of
course, its a derivative of *aus-ro- 'dawn, morning', from the "Eos/Aurora"
root *h2aus-. I haven't come across <dziennica> or the like with any
kind of astronomical or mythological meaning.
Piotr