Jane Foster thor would lose without mjolnir imo. Remember, she is just Jane Foster, everything she is doing is literally Mjolnir not only giving her that power, but telling her how, and when she can use it.
Jane herself has littke fighting experience compared to supergirl. And its a slugfest ( like pretty much all supes vs. Thor threads tend to be). Which imo is full tilt in the Kryptonians favor.
But equalized stats pretty much and they are just brawling.
Guess it could really go either way. Supergirl is way hotter though.