I honestly believe everything would be fine. BUT, if it will ease both of your minds, skip the placebo's and start immediately with the new pack, with the ole adage, better safe than sorry. There is no harm in doing so and if it will ease both your worries than that is better than being stressed out for a month. She did start on an off day, had her period mid pack, etc.

That seems to be the best option for the both of you, IMO.