Had the woman taken an NSAID? - perhaps she had an epis or tear? This article highlights the lack of knowledge and reseach surrounding postnatal hypertension, and suggests a link between NSAIDs and raised BP:
Postpartum hypertension and nonsteroidal analgesia
American Journal of Obstetrics and Gynecology,
Volume 190, Issue 2,
February 2004,
Pages 577-578
Angela Makris, Charlene Thornton, Annemarie Hennessy