I wouldn't expect anything at all from my ex-stepfather with whom I didn't see eye to eye.

Can't quite see why you've been invited but if it's your ex's way of continuing to be on good terms with you, then that's sweet of her.

Perhaps a card to the ex step-daughter and a little note to her Mom, thanking her for the invitation, and subtly congratulating her on her achievements as a mother...something along the lines of 'I'm sure you must be so proud of her - seems like only yesterday she was...' doing whatever it was she was doing that you'll both remember - you must have at least one happy memory of her growing up.

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