No, one of the main problems here is that people also pull on the bit while they neck rein because their horse's are not properly trained or the people don't know how to ride. When you do that, then yes, the signals can get confusing because you are cueing for a left turn with the right rein but also pulling on the right side of the bit and cueing for a right turn. Very confusing, especially to a young horse. So long as the reins are left loose, neck reining in a snaffle is a snap.
Plus, at breed shows, any horse that is ridden in a snaffle is supposed to be ridden with 2 hands and only horses 5 years old and younger can be ridden in a snaffle. All others must be ridden with one hand in a curb bit. At least that's how I think it is. It has been a long time since I was involved in the show world.
Also, I just wanted to add that if she was trained in a bosal, more likely than not, she would probably do better in a bosal hackamore or even a soft hackamore (rope halter). But for a beginning bit, the snaffle will be your best bet.