HCG 9 weeks postpartum?

Kirsten • Married October 2015. Welcomed TWIN boys January 2017 💕

My SISTER is 9 weeks postpartum. Had sex 3 weeks ago and is breastfeeding. she decided to take a test on Sunday and it was a very obvious positive on a first response pink dye. Had a blood draw hours after and her hcg was 5. The next two days she got negatives on clear blue digital. Today she had gotten two positives (or evaps maybe?) on 88 cent Walmart tests. Anyone have any idea what could be going on?