I had to look at some of my old stuff to figure out the answer.
Simply put the first 1995 release of Leia, as with the others, all came on that same square card you have pictured.
Ater the initial run which sold through the roof,(Leia went for upwards of $30 on the secondary market in 1995, alas no longer) Wave 1 was re-released with the new cut card backs you've been seeing on ebay and such.
I have two of the square cards left in my sale stuff(Han & Stormtrooper), that yeah are still hanging around since 1995
Since I've had a lot of difficulty selling those for $5-$8 each I wouldn't think the Leia has any more significant value.
You should also check if the Leia has two or three stripes on her belt and look into if that effects the value or not.
The ohter main difference with the two styles is that the square card features a larger bio card than the Vader cut out version does.