I would add that we have a significant number of students who have to overcome "nose breathing," and some deal with that issue for the first time in the open water pool sessions. I find most deal with it quickly and without problems. It's important that dallaskinkaid's girlfriend not over think the problem. If she needs to "practice" mouth breathing, she can do that without a snorkel. Just put on the mask and talk and do other things normally. There may be a cheat or two, but getting used to the mask on her face is probably a bigger deal than breathing through her mouth. Tell her the issue is VERY common, and she should not be worrying about it.
DivemasterDennis