It could be that her species has a closed circulatory system, one that does not create new blood as it does not "age out". In a system like this bleeding would be beyond deadly with out an immediate source of transfusion. These systems also resist the active leaking of blood so one would not "see" her bleed. Her system would isolate it's circulatory functions to prevent this from happening.
Jaivette the RN and all round alien physiology geek. I even did a pseudoscientific paper on Kryptonian Physiology and created a race of biological comparable humanoid marsupials.
(ithinkineedalife)