I can fill in some gaps in this! There was a portal between the b1 universe and the b1 incipisphere universe in the frog ruin's on grandpa harley's island, which not only allowed grandpa to freely travel the beta kids' planets during their time and then leave, thus returning to a time before his death, retrieving jade's dead dreamself to his island. Now, potentially, the same or similar portal allowed for condesce's initial entry to b1 earth, before having to leave and being enslaved by english

She was enslaved by English long before she went to Earth.  She was the farthest she’d ever been away from Alternia when the Vast Glub happened, killing her Helmsman.  It took her 612 sweeps to get back. Then the Handmaid appeared on her ship from Alternia’s Green Moon.  )(IC killed her and began her work under LE.  Her job was to be his “emissary” to go to the places he is unable to reach himself. Much how Doc Scratch allowed Lord English into the Trolls’ Universe it was the Condese job to let him into the kids’ universe.  That’s why she’s there.  As to how she got there, she probably flew.  The Green Sun intersect the universes.  The trolls flew the meteor there to rendezvous with Dave and Rose before going to the Alpha kid universe.  So despite being incredibly difficult it’s entirely possible.  

~Mod T