Five months between OW class and first dives is a long time. It will be like learning to dive all over again. You might want to think about using that lake for some dives to keep your skills fresh ... Maybe find a more experienced diver to go with or look at the shop you certified with for a DM for hire. The more you both dive (just for fun), the more comfortable you will become. If all you dive is in a pool, you will be an expert in the pool, but a newbie in open water.
Mastering any scuba skill in four days is completely subjective. The fact that you are diving infrequently will only elevate the issue. Your instructor may have witnessed her doing it comfortably, but that doesn't mean she will master it a week from now as it is still a newly acquired skill.
The question you have to ask is should her mask be dislodged, is she going to panic and bolt to the surface. Doesn't matter if it is cold water or warm water, in a situation that is most likely going to be an accident and happen 'all of a sudden', how is your wife (and you as her buddy) going to react. Accidental mask removal is never a planned event.
Think about all the skills you learned in a non linear way. Why would they teach you these skills -- not just that you are learning them and the respective steps to complete them. Visualize the scenario(s) and how you WILL react to it (them). It could be a scenario as simple as defogging a mask or tearing open a high pressure hose.
Hope this helps,
jcf