Traxex Here

1 level of frost arrows is enough to orb walk enemies, so there isn't a huge point in mass levelling it up early, you need to max precision aura early as well and i prefer 1 level in silence at 4 (some pros get stats at 2 or 4) i put stats at 5 as all of your skills are maxed out at this stage and drow really benifits from at least 1 stat level before 6. I think that daedelus late game covers getting a crystalis, HoD and manta are more important at that stage to give more survivablity as drow has no escape and no hp regen in this build, also, getting HoD and manta rather than crystalis early allows you to dominate an alpha wolf and give its perks (i think it gives the damage aura to illusions, i'm not too sure on that one).

you should add crystalysis to core

Edit: also, whats with the random stat point at lvl 5.

thats why MoM is situational and HoD is core, and honestly MoM+bkb isn't that bad unless your against heroes such as faceless void

Mask of Madness isn't really an item for her, better get Helm of the Dominator and later upgrade it into Satanic. Way better damage, health and lifesteal.