First - welcome to the Forum! I think you'll find lots of interesting stuff here. It's inhabited by some decidedly eccentric characters, but most of us seem to be relatively harmless.
I'm reasonably (though not a hundred percent) certain that the Revell and Heller Nina kits are identical.
Revell originally issued its Santa Maria back in 1957. (The date is from Dr. Graham's Remembering Revell Model Kits. It was the company's third sailing ship - after the Constitution and the Bounty.) Heller's, which was about the same size, came quite a bit later - in the late sixties or very early seventies, if I remember correctly. I think the Heller Nina and Pinta came out at that same time, or nearly so. I first got acquainted with them when they were being sold in the U.S. under (I think) the Minicraft label.
Some time in the late seventies or the eighties Revell and Heller worked out some sort of arrangement whereby some of their kits appeared in boxes with each other's names on them. (I remember seeing the Revell Flying Cloud and Mayflower, for example, in Heller boxes.) I think that was when Revell started selling its Nina and Pinta kits. My recollection (which obviously is pretty hazy - as it often is these days) is that the only appeared in the catalog of Revell Germany. (The comprehensive list of Revell kits in Dr. Graham's appendix doesn't list either of them; the list only covers the products of the American company. On the other hand, Dr. Graham's coverage stops in 1979; if either of the kits showed up in an American box after that date, it wouldn't be on the list.) Maybe some other Forum member who's actually bought the kits can correct me, but I'm pretty sure the contents of the Revell and Heller versions of the Nina are essentially identical. If you've got the Heller one, you've got the Revell one.
I remember building the Heller Pinta. I recall it as a nice kit; though next to nothing is known for certain about Columbus's ships, the Heller reconstruction looked pretty reasonable. Be warned of one point, though: the Nina and Pinta kits use the same hull. Since we know so little about the actual ships, that doesn't make much difference - unless you display the two models side by side.
Good luck.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.