I don't know what would cause your retriever to stop retrieving but I know what old school Labrador guys would say and it's not going to help your situation, so let's get it out of the way with the first reply.
- Labradors come in three colors, red not being one of them
- Labradors should be bred to retrieve first, then flush- not point
Okay, now that's out of the way. My advice is just work with her on retrieves, starting easy and making it fun again. Start with the basics, let her enjoy the game. Don't progress until she is retrieving and holding to your satisfaction. My guess is she will snap back into her main role. Maybe too much work in the upland fields "pointing" has her identifying as a short hair.
I don't think a Lab in her prime will completely forget the drive to retrieve.
Force fetch as a last resort.