I guess it wouldn't be! Because the only reason it's a forbidden love it's because Edward is a vampire and she's his forbidden fruit!
So if she for any reason ended up with Jacob it wouldn't be forbidden:D
It can be classified as forbidden love if she chose Jacob because technically Jacob is a werewolf and she is human. But, werewolf's are "allowed" to date humans (Sam and Emily for example) It basically depends on the way you look at it.