Remember that it is HER decision whether she accepts your invite. Please don't pester her to do so. You might just be saddling her with crippling anxiety. Just because you ask her doesn't obligate her to accept. I am sorry if I sound rash but this sounds dangerously close to you obsessing over this and trying to strongarm her into going is tantamount to abuse. If you value the friendship, simply allow her to say "No" and simply advise her that you are available to talk about it later should she want to. Again, don't be pushy, whether it be getting a yes or getting her to open up about a problem she might have. A friend would be accepting even if it is not the answer they want.