The purpose of this research study is to find out whether women with severe preeclampsia taking low-dose aspirin (LDA) for 3 weeks post-delivery will experience an improvement in endothelial function (measured as flow-mediated dilation - FMD) and severity of disease, as the effects of preeclampsia can persist postpartum. Women diagnosed with severe preeclampsia prior to delivery will be enrolled and randomized to receive either low-dose aspirin (81mg) or placebo to take daily for up to 3 weeks post-delivery. Exploratory objective includes healthy control postpartum patients without preeclampsia and not on LDA during pregnancy or postpartum in comparison with the primary study population affected by preeclampsia with severe features.