I am a new landlord (for 6 months now) and I have a tenant that has progressively gotten worse on paying her rent. She is currently past due and I sent her a seven day notice via certified mail with a return receipt requested. She was not at home when the delivery was attempted and the usps left a notice telling her that she has a certified piece of mail at their office. Its been four days now and she has not picked up the letter. When does her seven days start? Is it when the postal service attempts the delivery or when she actually picks it up?

If in the US, what state, laws very by state.
Do you live out of town, is that the reason you mailed it ?

The state is Kentucky. I live about 30 minutes away but the reason I mailed it was because I had read many comments on threads throughout the Internet suggesting to send it this way so that I would have proof that she received it.

Most landlords just hand it to them or tape it to their door. Perhaps a witness to see you do it, photos of you doing it. Most people who are dead beats don't ever sign for registered letters

Thanks. I'll get a witness and hand deliver it. Should I just give them a copy of the original 7 day notice or start a new one?

The 7 days (or whatever the period is in Kentucky) will run from whenever she is given the notice. So do a new one.