It depends on who you are sending the PM to. Some ladies don't log in here that often so don't receive the PM. When they do they may have hundreds of PMs sitting in their in box. You can't expect them to reply to every PM in such cases - particularly the older ones as they will probably by that stage be working in a different part of the country.
If the lady does not log in here often just pick up the phone and ring them. It's the quickest option.