What do you mean that when she can see them she will break. Is she sight pointing or pointing off smell? How broke to you want your dog?
Get her "whoa" broke, and then put her on a barrel. Get the barrel off the ground and get your pigeons. You can teather them like Machia said or just remove the flight feathers from one or two and let them walk around the table. Make the dog "Whoa" at all times..... The dog will eventually get used to it and will relax, and watch the birds walk around..
You can also get a bird launcher. Put a pigeon in the launcher, and work your dog into the wind until it points. The second the dog tries to flush the bird launch it and don't shoot. The dog will learn that it can't catch the bird. Also, don't shoot unless the dog does is perfectly.................. You might have a tough time getting your dog to point real staunch and hold birds though. The GSP side will do it, but the Lab side is going to want to flush the bird every time. This is one reason cross breeds pointers/flushers are tough to work with. You have two seperate instincts in the dog pulling in two opposite direction... But I wouldn't worry too much yet, a 3 1/2 month old pup is still a baby. Birds are still play toys and ment to be chased, caught, eaten etc..... Give your pup time to develop and dont push her. At this stage in the game she should just be having fun, bonding with you, and slowly building that prey drive. Putting her on birds will build the drive, but don't expect too much from her until she gets older and matures..