if she had right of way and witnesses , you are screwed . even if she is obviously speeding or not paying due care its pretty irrelevant in this case . my wife changed lanes and a guy hit her from behind sending the car accross 4 lanes of trafic and writing it off . he was obviously speeding and police acknoledged that but its his lane and his right of way , you have to prove you wernt there , not how fast shes going.
your only hope is to get a couple of witnesses at the scene to testify 100% that you did not pull into her lane and even then youd probably need some physical evidence of such cause her insurance company will fight it all the way especially as shes got witnesses .
if you got insurance bite the bullet and pay the excess . talk to your insurance company but id say they will give the same advise