My advice, call her tonight and decisively tell her in no uncertain terms that is over. Do not make excuses. Do not beat around the bush.
I would not initiate contact. If she contacts you, politely state this "I believe it is best if we ________"
You can fill in the blank.
Do not justify your answer. Listen to her and validate. Then follow through with whatever your blank is.
This reminds me of something I read about being assertive as opposed to passive or aggressive - I think i can fall to passive.
Assertive: Be Firm, deliver the message clearly, use I statements, be a broken record (say "no thank you" and then keep saying it over and over and over), and have good boundaries.
