I've just cought an Eevee on Pokémon Black 2. I know I wont be able evolve Eevee yet but when the time comes, how can I evolve her?
You have to raise it to max happiness then level it up at night.
Same as in all the other games. Eevee's happiness must be at its max. Evolve her at night with max happiness, and she should evolve!
Source: experience
you need to evolve it at night and make its happiness go up by feeding it carbos and puting as the lead of you party and battling Do NOT feed it herbs or make it faint it will make its hapiness go down. I hope I helped.