That was just blood pooling from her two more serious wounds to her hip an her head as her body laid there for over an hour IIRC on the time.
I am more interested in the blood pool where she was shot and sat as OP tore the door apart, that was a tiny amount of blood for a gunshot victim with 5 massive wounds including 2 severed arteries. If she had survived for even a minute with those injuries the entire WC would have been covered with a massive pool of blood.
For example, if you do not mind the very graphic image of seeing a man get shot only in the head, and unlike Reeva he survived for a short time with his heart still pumping blood, then Google this:
bangkok protester shot head, bleeds out liveleak
In the US it is the first result at the top if the page. Warning: very graphic!
You're forgetting her head ended up over the toilet, her gunshot wound bleeding out directly into the bowl. I'd imagine the reason for the relatively small amount of blood (still looked like quite a bit though) was that she lost most of it in the toilet.
Personally, I've seen enough bestgore and watched enough trials to need to google a bit of gore *advertiser censored* to know how much blood the human body contains or how much a gunshot to the head bleeds.