Thanks for the query.
Some amount of disparity in the gestational age
can be seen in ultrasound
If the ultrasound report is accurate, there could be some irregularity in her cycles.
And the bleeding she had on 11th could be post-coital bleeding.
If the ultrasound is showing some days disparity then the bleeding could be implantation
Few days of disparity usually won't affect the time of expected date of delivery much.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429