That is ABSOLUTELY the wrong method for determining board size!!!!! Forget that method, it's garbage!
Go to the board manufacturer's web site and check the weight/size range scale for the model(s) you/your wife are interested in! Same for your daughter! Although for her you may get away with sizing up a bit if she is still growing significantly year to year!!
I understand the method is not the end all... but I have to have some type of reference point. Because of her weight/size and skill level I think a 138 would be the right size for her, but thats my opinion