The best wedding I ever went to (and I have been to many) was close friends and family only - a registry office, followed by a casual meal in a local restaurant and then back to the happy couple’s house for drinks, dancing and late night pizzas.
Just pick an appropriate place for the group without her and say that hopefully there might be one extra and ‘Sally’ might make it but if so she’ll sleep in the sofa bed / airbed / she’ll share with you etc.
