They are wonderful bikes! I think that Puch is correct...
I've had several over the years and this is my latest: http://www.bikeforums.net/showthread.php?t=437245

Does hers look similar to this? If so, clean/lube and ride it. I wouldn't modify it much if I were you... They are making a nice comeback and you can easily get a nice chunk of $$ jing if you ever want to sell it, seriously.....

Clean off the rear 3 speed hub (they shine up nicely w/ degreaser or even dish soap w/ a little bit of hot water, just wipe it dry right away) and look for the 2-digit code. That will be your year. How about some photos?