Eluned can be found travelling with Islwyn teleporting between the magic trees outside Lletya and the clearing north-east of the Tyras Camp. Eluned is involved in the Roving Elves Quest. She will recharge your Teleport crystal for 150 - 750 coins. She will only do this if it is out of charges. She will also recharge more than one at the same time and if you have not recharged your 5th yet she will tell you the prices of the 1st - 5th crystal she recharges and it will act just as if you recharged them one by one.
See this for a detailed map of Isafdar, which shows the paths to Eluned and Islwyn and the traps and obstacles along the way.
Eluned, as mentioned above, teleports around between 2 locations. A quick way to find her is to go to one of the locations, and then either wait 5 minutes for her to teleport to that location, or world hop until you find her.
For those seeking Eluned for her step in a hard clue, players need only start the Regicide quest to interact with her (although finishing the quest to unlock the charter ship is strongly recommended).