I thought that naproxen was contraindicated in the third trimester of pregnancy?
We had a patient with a similar condition during clinicals- they sent her up to the surgical floor a few days after she delivered. The lactation consultant and all the other support people came upstairs to her
It sounds like a conference with all of the caregivers (internist, surgeon, obstetrician, etc.) would help.
I hope that your sister feels well soon.