Thanks for the additional information.
It's possible that she was in heat a few days before the discharge developed although it doesn't particularly matter if that's the case. A dog's cycle is broken into various phases:
Proestrus, estrus and then diestrus. She most likely would be in proestrus if you've just noticed her bleeding. Let me go through each phase so you'll know what to expect:
Usually this phase is associated with varying quantities of a bloody vaginal discharge...and the blood can look quite red and fresh (as you are seeing). The volume most definitely can vary from female to female; some produce a fair amount while others barely produce any blood or just a few drops of it. Since many females will also lick their vulvas in an attempt to keep themselves clean, it can often be difficult to quantify the amount of blood produced.
The vulva slowly increases in size throughout this phase of the cycle.
In terms of behavior, many females will become more playful (although this may be hard to determine since she's still so young). Some dogs will become grumpy and not want to interact with their families in quite the same way as they did before they were in heat. Again, there's a great deal of variability about this from one female to the next.
Proestrus can last anywhere from 6-11 days with an average of 9 days for most females.
In some, but not all dogs, the vaginal discharge fades or reduces significantly in volume. It may change in color to a more straw-colored or clear color.
The vulva remains swollen.
In terms of behavior, if there's a male around, then they may try to mount the female and she would be receptive to him (which would not be the case in proestrus).
Some females will go off their food during this phase and can remain out of sorts.
Estrus typically lasts about 5-9 days although it can vary quite a bit between females.
This is when females are out of heat. Vaginal discharge is no longer present and females are no longer interested in males.
The vulva will slowly decrease in size.
Behavioral changes (if present) usually return to normal.
It sounds as if the amount of blood that you're seeing is normal for a female in heat and that her behavioral changes could also be consistent with it.
But, having said that, dogs can have more than one issue going on at one time. I might take her temperature since a female in heat should not be running a fever. Normal is between 100 and 102.5. If it's elevated, then there may be something else going on with her which would explain her being "off".
I hope this helps. Deb