I, too, have a female doberman that went through the same thing. She's almost 4 years old now and for the longest time she was always "leaking" around the house.
I talked to my vet about it and they prescribed a medication called Diethylstilbestrol (DES).
When she first started taking it, it was a capsule a day for a week, then every other day for a week and now she only needs to take it once per week. The results are amazing and we saw a difference rather quickly. It's very inexpensive, too. I can get 20 capsules for $16.00 at my vet's office, so it's about $0.80 a capsule. A VERY inexpensive therapy to help with this problem!
He said this is a common effect of females who have been spayed because they lose their ability to "pinch off" a tube on their insides so they end up leaking (no fault of their own, they just can't hold it in). He said it was commonly used a long time ago in pregnant women (I can't remember the reason they used it), but it was causing birth defects in babies so it's since been stopped for use in pregnant woman. He told me that pregnant women should not even handle the capsules because of that risk. So if you do happen to get these pills, be very careful with them.
I have been very pleased with the results and she no longer leaks. I just put in with her breakfast in the morning once a week and she doesn't know it's in there. I used to give it to her in cheese but she started to figure it out.
Good luck with your girl!