As with all the bosses in this game, you only need to do 1 thing: TYPHOON!
Seriously though, max out your typhoon as soon as you can. On "Give Me Deus Ex" difficulty, you can drop this gal, and the other bosses as well, with 3 typhoon hits.
All you need prior to any boss fight is:
1.) Maxed out Typhoon
2.) Typhoon ammo
3.) Energy bars
Yelena is at the end of the Picus mission. She has a tendency to go invis, but she will run right at you in the beginning and make this an easy KO.