Just asking here, but how old is the birth certificate? Over the years, Peru has been moving district documents into a more centralized (RENIEC) system. If it is a certificate that mom's had lying around for several years, I would suggest getting a new one straight from RENIEC. Not sure if they are still around, but a few years back you could get one issued from a kiosk at Jockey Plaza (among other locations).
Does the top left of the certificate have a bar code and number, "Republica del Peru" in the center, and the RENIEC logo on the top, right?