t. Vigilance! I'd not get comfortable at 3 weeks, it could run past a few days. Females can be different and I've had successful breedings past 20 days.
If it is a NAVHDA test, you need to inform them she is in heat.
I have it figured as you should keep her locked down until the 7th-8th of Sept to be on the safe side.
Yea, some dogs act different during their heat cycle. SOme dont. Mine is a complete freak during it.
Great advice from Mstand and PD. You said this is her first heat? Do you plan on breeding her, in the future? If so I'd follow there advice.