1). Too early to see anything on sonogram. Levels need to be 1000 or higher in order to see sac. So in 4 days you probably still won't see anything. I'd wait 2 weeks.
2). It could be a chemical pregnancy.
3). Doctor's urine tests are not as sensitive as the ones you can buy.
4). Bleeding during pregnancy doesn't always indicate a problem but may support the theory she is having a miscarriage.
I wish you both much luck!
I would say it could be a CHEMICAL Preg, google it and look into it, i just had one. I got a Pos preg urine read 17 days after i Misscarried, when a Mc is this early it is considered a Chemical preg, meaning you can not see anthing on the sono only chemicaly, meaning urine or blood sometimes what happ is you get a pos read and then it fades as you lose the baby, i believe with a Chemical preg, the baby is not able to implant it self into the lining of the uterus, but you get the a post read. Google it and see if it matches up what you are saying.