Really means, “I really feel bad BUT if I can’t go then you shouldn’t want to go without me.”
If you go without her, get ready. You will get the “Did you have fun without me?” question. To which the correct response is “Of course not! I was miserable without you. I shouldn’t have even gone.”
Throw in an “Everyone asked about you and wondered why you weren’t there”. Regardless if they did or did not say this. This makes her feel like people actually acknowledged she wasn’t there.