please dont' give her anything in writing tomorrow. she cannot hold you to ransom like that. call FRAL now - they may still be available.

IF you feel an need to put something in writing, put it only for a limited time frame - say december/january PENDING DISCUSSION WITH CSA. i would be VERY reluctant to sign anything for her though. try FRAL now. please
if she is going to try and stop christmas access, they might have a parenting advisor or something that can give you immediate advice.
don't quote me, but they may even be open for calls saturday mornings (i can't remember the times from referring at work - haven't been in a while!)