if you go, you dont have to do the communion or anything like that... you could consider getting wireless earbud headphones and a mp3 player or walkmen.... just put one of the wireless earbuds in your ear thats facing away from your friend, and you'll be fine... if anyone else asks, it's a hearing-aid
i dont think you said so, but are you catholic? or what would you associate yourself to mostly?
you could allways say your leaning towards another aspect of chirstianity side and say it would be best for you to do your religion on your own, sleeping in your own bed till noon that is... but for real, not all religions require you to attend every week...
... if you talk to her and express yourself to her, she has to accept it... yet again, maybe there is something you can get her to do for you going...