Megan, I, too, am new to 12 ownership. It's an 1877. The needle plate has one screw, and does lift off. It is a very snug fit.
What you may want to try: kerosene or charcoal lighter fluid dissolves old oil, and is generally safe on finish where the clear coat is not compromised. Using a screwdriver, insert the blade about 1/8" into the kero, and gently apply the dampened blade to both sides of the needle plate seams, left, right, upper, lower. Repeat a few times, let sit, repeat again. Let it work. half a day, a day, repeating.
If the kero has not budged the plate to be removed by hand, you could: remove the needle, foot, and screw. Position the shuttle carrier so it is out of the way of the needle plate. Carefully, using a long small block of wood, about the size of a pencil, position one end against the underside of the needle plate, and gently tap on the other end with a lightweight hammer. GENTLY so as not to damage the needle plate.