I think thats 18 days ago .. ; ^)
That's 16 days too long .... the house could have been show shown 10 times, 20 new buyers could have been introduced to the home via showings, etc etc ...
Anytime you have a home for a sale, every other day is just about right, even if it's a 2 minute conversation or a short 1 sentence email..
Call the broker and tell him/her you are canceling the contract, give them the reasons - and you'll be sending the "reasons" certified mail ... keep in mind, the broker hates to lose business, so you'll hear a lot of stories.
That said, send a letter with all of the proper dates and times ... in this case, it will be a short letter.
Just make sure you interview 4 or 5 agents and get their historys and experience so this doesn't happen again -- this isn't rare.
Sorry to hear about your bad experience with your current Realtor. Before you terminate your contract, call the Broker's office and speak to the Manager. Make sure to point out the reasons you are frustrated with her and if possible do it in writing as well. Communication is a must in Real Estate. Good luck!