This is tough one.For future relationships youve got to keep her in.Does she have to come to the shower i dont know!!! does she have to be at the wedding? yes she does.
Now quite honestly she may really not want to be there,but theres no way your going to win this one she was very quick to go and report back to the inlaws.
I think your going to have to kill her with kindness maybe via the inlaws and your husband to b.
What was you asking of her as far as being in the wedding party?
Dont let her ruin your planning or day But you must remember you are the better person so dont give her the ammo to turn you into BRIDEZILLA lol
Calmly ask her want she wants to be involved in VIA the inlaws ask them to ask her as you really dont want to upset everyone (see killing um all with kindness) and go from there.Smile,you will sort it out xxxx