The white-haired witch needs to spend a standard action to maintain the grapple at the beginning of the next round, if she succeeded in hitting (and thus grappling) a target, and the target failed to break free. – But what if an Attack of Opportunity is provoked before her next round? Can more of her hair (eyebrows?) stretch out and attack? With combat reflexes and high dexterity, at high levels she'd be threatening a large area. What if she hit say 3 enemies (1 on her turn and then 2 AOs since), all now grappled (while she's still not in the grappled condition), now it's her turn again. Her spending a standard action to maintain the grapple, would that be for all 3 or just the one she grappled on her turn? Or would each new grapple end the old one?
"When a white-haired witch grapples a foe in this way, she does not gain the grappled condition."
I can't see anything RAW keeping her from grappling more people.
Best Answer
You can grapple multiple targets, but only until your turn.
Looking at the rules, I see nothing that disagrees with your idea that the witch can start extra grapples with her hair using attacks of opportunity while she grapples someone else. As you note, it takes a standard action to keep someone grappled, which means that unless you find a way of generating extra standard actions, you can only keep one opponent grappled once it's your turn. The others go free.