My wife started using birth control pills a week ago. She stopped for 1 day and now her period is lasting longer than normal. Is this because of the p?

Possibly. Just keep going. Stay with the pack, periods may be irregular for up to 3 months when you just start a pill. If she skips a day, take two the next day. If you skip 2 days, still only take 2 pills on the day you remember and use a second form (condoms) for about 10 days.