There is quite a bit of confusion about grappling and its relationship to the other combat manoeuvres. Tarathion provided a helpful link:-
http://paizo.com/paizo/blog/v5...pon-Special-Features
Grappling is not an attack action. By default, it does not benefit from Greater Magic Fang. There is a feat called Weapon Focus (grapple) which adds +1 to your grapple checks.
http://www.d20pfsrd.com/feats/...focus-combat---final
However the presence of this feat may be a holdover from 3.5 D&D and might not have been considered in the change to Pathfinder.
http://paizo.com/threads/rzs2nnre?Weapon-focus
There are a few grapple weapons such as the mancatcher. Presumably a masterwork/magical mancatcher would add its enhancement bonus to the grapple check, although this is never explicitly described.
The white-haired witch's hair attack is not an unarmed strike. It is a natural attack.
http://www.d20pfsrd.com/classe...s/white-haired-witch
Greater Magic Fang can be applied to the hair. At caster level 10, this gives a +2 bonus.
"Grab" is described as a special attack. As such, I think that it is reasonable for enhancement bonuses and Weapon Focus feat on that natural weapon to also apply to the grapple check. However this is not explicitly mentioned anywhere.
The guided weapon enhancement is a magical enhancement that can be applied to weapons. I am not sure how a witch could apply this to her hair. The guided weapon is not in the Pathfinder ruleset. It was published by Paizo for 3.5, before Pathfinder was released. It has not been transferred into Pathfinder. (Indeed the reason that I don't have weapons with this property is because it is not part of Pathfinder.)
http://www.d20pfsrd.com/magic-...on-property---guided
Some people regard the guided weapon enhancement as overpowered for clerics, druids & monks.
http://paizo.com/threads/rzs2l...hantment-overpowered