So my wife has been a very heavy sleeper for all her life. We have just had a baby, and his crying doesn't wake her up. I don't mind getting up in the middle of the night, but there have been times I do not wake up to his crying too. I've fixed my problem by setting alarms which wake me up.
There is another problem(?) she "wakes" up and does stuff but, in all reality her mind is still sleeping. We could have conversations that she won't even remember. She would get up and do things, like if she would be awake. Her "sleeping self" (which is what I call it) fights with me, but she has no recollection.

So how can my wife become a light sleeper?

The emergency is, what happens if I am not there. I cannot tell the future, but we like to be prepared.

I don't even think she has lucid dreams very often either. If that helps.