Yahoo contacts no longer syncing?

We have two iPhone 5s, my wifes and mine. Yahoo contacts weren't syncing

correctly a while ago with our iPhone 4s, but when I upgraded to iOS 6 it was

syncing ok. Then it continued to work on our iPhone 5s (until recently)

Now my wife's iPhone 5 has stopped syncing the contacts with Yahoo.

I have tested my phone and it is syncing both ways almost immediately.

The settings are identical on both phones as far as I can tell.

I have backed up her phone to our computer but I'm not sure what to do next. She

has made a lot of changes on the phone which have not been saved to Yahoo.

If I disconnect Yahoo and reconnect it might reset the sync and fix that, but we

will lose all the changes she has made, right?

If I then restored from the back up would that restore the contacts?

Or could I back up contacts to iCloud? Then later go back to syncing those same

contacts with Yahoo?

Any help would be much appreciated.

Jeff