I feel for the step mom in this situation. She’d probably been looking forward to choosing a prom dress with her daughter for a long time. You did put her in an awkward position. Sending a card to her with her daughter’s photos, stating 'our family' seems insensitive and a bit of a slap in the face to a woman who has been kind and supportive to you. As for the tampons….definitely a no- go area for a step mom, at least without mom’s permission. I feel like your excuses are a little disingenuous. You get to be the fun one while she does the hard work and that’s threatening. I think you should heed her warning to back off a bit.