My Vampire Kingdoms sourcebook says Erin Tarn has not been heard from since her expedition into— well, the vampire kingdoms— but I'm fairly certain she made it out alive. Am I mistaken? and, if not, how did she?
If you read Erin's letter entry at the beginning of Wormwood, you find out what happened to her. Essentially she enters Mexico, sees that it's worse than anyone had imagined and due to the overwhelming amount of vampires and the high heat she agrees to allow a Mexican ley line walker to attempt a portal travel. This lands her in Wormwood. After a long tour with Lazarus and The Confessor, she eventually hops a portal to England and starts her European tour. You should check it out, it really is a good read.
I don't think that there's any specific canon answer, but it's somewhat implied that the Coalition inadvertently rescued her. In Rifts Underseas, when she is attacked by the slavers with the Lorica Wraith, she claims that "This was not the first time, nor the last, that the Coalition would rescue me from almost certain death."
If not, the whole "Erin Tarn is missing," thing might be supposed to be an inspiration for a campaign into the Vampire Kingdoms.