If you are using a normal remote , I suggest you to continue training her at pine forest , but go for the cirrus with different element , they give slightly better exp I guess . If you are using e-remote and you do have an earth character in your team , you can cast stone wall on Elin , which means you can basically train her anywhere .

Of course , if you can afford Training Vouchers and Exp potions .. :) That would be the fastest way to lvl up Elin .

Here's some links on how to train pets

>>> http://wlodb.com/topics/4645 <<<
>>> http://forum.wl.igg.com/viewthread.php?tid=49791 <<<

But in my opinion , since Elin has naturally high CON and hp , she can survive better than any other pets .
My personal suggestion would be :
Pine Forest --> lv 30
Oslya --> lv 50
South Pole --> lv 70
Japan Troll cave --> Lv 90-100
Rome Pangolin/Leopard

** Training at Oslya give different kind of meats , you can simply cook them and voila ! You can save some money from buying hp foods . The same goes with South Pole . In my opinion , South Pole is a training paradise .The mobs give cods and salmons which can be cooked and they also gives wolf tooth ! :))) Which is rank 20 , you can either sell them to the npc or to the player and earn some money from it . Next , the mobs in Japan Troll cave also gives cod , if I'm not mistaken . Last but not least , Pangolins at rome gives decent exp but unfortunately they don't drop any meats or fish :/ . Also , the pangos have a lot os spawns so you get better exp. The other option besides training at pangolin would be leopard in athens , here they drop meats.But the spawn of leopard is not as many as the pangos and leopards do much higher damage :( .