Believe me, she will just know when it starts, i used to be told that all the time and think 'how?' but when my contractions started there was no doubt it was the real thing! (although my partner didn't believe me and stayed at work nearly all day!)
I believe a burst of energy is quite common, the day before I went into labour I cleaned the house, washed mine and my partners cars (he helped!) and went to the supermarket for a weeks worth of food.
MW will write in her notes how far engaged baby is 5/5 means not engaged and 0/5 iswhen you're in labour.
Braxton Hicks may start to get stronger or occur more often and she may get a 'show' although this can start a couple of weeks before anything happens!
Good Luck and enjoy!!