elin is non busrtable. :\ you need assit skill for pet to be burstable.

yes its possible to use her as a cow (or any other pet without assit) and get her lvls that way. but it'll be slow and you won't get over 200-400exp non and double exp day.

i've known people to get their roca up to 50 and their cow up to 100 doing this putting a weight on the cows (and pets). but after a while you need to move up to a higher lvl area to get more exp again it'll still just be 200-400 and slooooowwwwww... will take you a few months to a year to get any progress.

so it's faster to train pet with you and combo at any lvl area or training island.
will take 2-3 months non stop training. even 2-4 if you just train on double exp alone. depending on where you train type of potions you have or how hard you can attack for its even possible to do in about 1 month.