If your girlfriend wants a stable language for iOS development she should use Objective-C. Apple have been very clear about the fact that Swift is evolving and that there will be breaking changes.

Changes to Swift are hardly indecisive or pointless. A very clear rationale for removing the ++ operator was laid out here: https://github.com/apple/swift-evolution/blob/master/proposa....

While these changes may be painful now (though the removal of the ++ operator seems minor to me), they should result in a stronger and simpler language in the long run.