When I am sick and I hit on the right remedy, I become really sleepy. I often take a nap. I look for sleepiness in my boys as a sign of making a good match. After being miserably uncomfortable, they have often fallen asleep in my arms i n under three minutes. Keep in mind those these are connections I've made for when we are ill, and when rest is often so important.
I don't know how I would react for a non illness sort of remedy, such as what your mil is using it for. I wouldn't expect that a remedy would cause wakefulness, unless as ASusan said, she took too much.
When I first started homeopathy, I followed the bottles instructions. I ended up "proving" my son, causing him to get more sick with the illness than when he started out.
Now, I give a remedy, if I see improvement within 15-30 minutes I leave it alone until I see the problems return (this could be in an hour, 4 hours, 24 hours, etc). If after 15-30 minutes, I don't see improvement, I give the remedy one more time. If I don't see improvements I look for another remedy. This is my main pattern. Keep in mind that I use energy testing to refine this so I can "cheat" a little and find individual matches a little easier.
If you are more curious and want to read more about this, there is an acute homeopathy thread floating around here somewhere.