I definately wouldn't go to either the shower or the wedding. I wouldn't send a gift either. And why did she invite you in the first place? She was probably just hoping for another gift, she couldn't possibly think you like her or that you'd want to go. I would send the invitation back and tick no on the RSVP. I dont think she'd care too much why you cant come.
And if the shower is at the office, just leave. I doubt she'll ask why you missed that either
plus she couldn't planning her own shower.
I think if you make up some excuse it's going to be very obvious. Sometimes it's best not to say anything at all. Maybe you won't even have to say you're not going to her wedding- just dont go. What is she going ot do, come back from the honeymoon like "why didn't you come?" oh please you know I dont like you already I still can't get passed why you invited me in the first place. Maybe she didn't want you to feel left out being the only one who didn't get an invite
