From the sounds of it, being honest with her isnt an option? (I wrote my dad - the source of my PTSD- a letter a few years ago outlining the abuse of my childhood and how it has impacted my life. I requested no further contact. I was a mess over it, got hospitalized, but it was so freeing)

Could you prehaps put her up in a hotel for her stay? Plan activities such as going to the movies, local museums and such. Places where you are together but the interaction is focused on external things that wouldnt require so much personal interaction between the two of you. Go out to eat for meals where conversation will be less likely to get out of control. or you could schedule appointments for yourself during the time that she is there so that your time with her is interrupted when you have to go off and do other things without her.

I think most important for you is to not spend the next month worrying about what is going to happen when she gets here. You are going to have to use a lot of positve self talk. Everytime her visit pops into your head you need to tell yourself that you will handle that situation when you come to it. You will only make it worse by worrying about it now.