It is in a waste vent in the Infirmary, part of the Research Lab north of the main base.
Drive there and pull away the meteor with the rover. Use the pressure chamber to squash you so you can squeeze through to reach the Infirmary door. Inside, grab the medi-hose and take it to the center hub of the rooms, then back down to the right to reach the Maintenance Area. Use the hose to wash the locator out, then exit through the BioWaste chute at the left side.
Once you have flushed the Locator Device from the vent, exit through the BioWaste hatch to your left.
She is hiding, trying to learn more about the alien artifacts before being forced to return to Earth. Drive to the Research station and you can recover the locator device that is tracking her. It is in the Infirmary.
To enter the Infirmary, you make yourself short by using the pressure device. To leave the Infirmary, there is a waste chute to the left in the maintenance area (where you find the locator device).
Despite the admonishing sign, the medi-hose is just what you need to flush the vent where the Locator Device is. Take the hose and go directly up toward the hub of the rooms. When you get there, come back down to the right, into the Maintenance Area. Use the hose, get the device, and exit through the BioWaste chute to your left.
Only Salerno still has a key card to enter the Rock Lab, but she can apparently get in without one. You only get a keycard when she drops hers at the BioDome. You cannot enter the Rock lab until then. Get the locator device from the Infirmary and you can track her down.
Lunar Colony
There are no guards at all on Lunar Colony. PASE doesn't have any money in the budget.
Once you leave the main moon base, your first stop is the Research Station in the upper right of the map. You can use the winch to move the meteor from the airlock. You will have to use the pressure chamber to make yourself flat and enter the Infirmary, where you will find the locator device for Cdr. Salerno.
Once you have recovered the Locator Device, you will find her in the upper room at the BioDome. But she escapes. Pick up her keycard and follow her to the Rock Lab. Get the geiger counter in the storage room (upper room at far right). When you use the counter to find the artifact, she will show up again.
Use the medi-hose to wash the Locator Device out of the disposal vent in the infirmary. Once you pick up the hose, you have a limited length, so you cannot go around the outside. Instead, go left and up to the center hub of the circular room, then down and right to reach the Maintenance Area. Use the hose on the vent and the Locator Device will wash out of the other end. (Exit using the BioWaste door.)
You will finally find Cdr. Salerno at the BioDome, but you will have to get the Locator Device from the Infirmary in the Research Station first. Use the pressure chamber to squash yourself down to squeeze through to the door.
Lunar Colony became the 29th island released in Poptropica (not counting mini-quests) on September 6, 2012.