I think just give her time to get her head around it. That's the benifit of a letter it gives the person time to think about it although I know it's horrible for you. If she doesn't get back to you by tomorrow maybe ask her if she wants to go for a drink or something then can talk about it then. Also gives u some control of what happens n u can distract ureself till then if u know what your going to do
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ps your not being irritating. People only reply on here if they want to
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hope things work out for you. Let us know how goes
take care