Other Earth is an alternate reality separate from the reality of the Marshall Family. It is believed to exist in an alternate quantum universe along a separate timeline than that of the Marshalls and is completely or wholly identical to their universe. Rick Marshall speculates on its existence as well to the existence of its own version of the Land of the Lost.
Both universes seem to be identical except for several details. In this timeline, Rick's wife never died, but he and his children, Will Marshall and Holly Marshall, wore separate clothes when they were lost into their version of the Land of the Lost. In trying to escape to their world, they became lodged in the Land of the Lost of their counterparts. Their Holly appealing to her counterpart in spirit form to free her father and brother. In tracking down his counterpart, Rick gave his counterpart the missing crystal to get home.
It is entirely possible Holly briefly glimpsed their Land of the Lost using the Keyless Pylon.