What causes high blood pressure in a female who just gave birth?

Pain, stress: Pain can raise blood pressure, so can stress.

Pregnancy: High blood pressure can be induced by the pregnancy - either as part of a toxemia (eg pre-eclampsia) or as isolated pregnancy induced hypertension. It generally improves but duration is variable and could last 2 months. Depending on severity , it may require treatment. Follow the advice of you OB or be referred to an internist or nephrologist or cardiologist.