Hi Eva!
I suggest you go take a look in the "Villager Trading Plaza" here:
http://www.belltreeforums.com/forumdisplay.php?85-Villager-Trading-Plaza
That part of the forum is dedicated to trading/selling/buying villagers.
You might find someone willing to sell or give Rosie away there!
Be aware that she is very popular though, so she will probably be sold at a high price.