A further sighting was reported on Wednesday in the same area, which teams are investigating.
“Our teams continue to follow up legitimate leads regarding the location of Samba, however, we have so far been unable to find and retrieve her,” said chief executive Laura Read.
“Our tactics continue to focus on deploying thermal drones, along with camera traps and humane traps aimed at tempting Samba out of hiding with favourite foods including melon.”
Zoo bosses say it is important the pair are reunited as capybaras are social animals.
The zoo has urged people not to approach Samba or attempt to catch her, warning this could “spook” the animal and push her out of the area.
Members of the public are asked to send photos or video along with the exact location of any sightings to help confirm them.