I'm going to be the bad person and mind read... No response means she is "confused." She doesn't want to be the one to end any possibility of going back on her decision. HOWEVER, this doesn't mean that she's planning on reconciling. She probably doubts her decision and your letter brings that doubt to the forefront. She's not ready to handle that. It brings up GUILT.
So going back to your deadline, if you don't keep to your promise you will come off like a push over.
M 42 H 39 T10 (-2yrs separation) S8 D5 DD 7/30/11 (EA&PA) Reconciled 6/2013 Separation in works 1/2017