My way would be to observe and befriend the group of primates and gradually befriend them.
The sudden removal is not in the benefit of the welfare of the girl.
A gradual process in several months would be more successful.
Time will show whether the sudden removal is going to work this time.
Why on earth would you think that?
Because animals in general (both male and female) start acting very violently when there's a child that starts secreting pheromones and looking like an adult. For monkeys in particular it's the beginning of fights between females that determine their future social status.
But the idea that monkeys would react to human pheromones is a bit of a jump. Especially considering the degree to which humans don't react to monkey pheromones.
It's a huge less bit of a jump than the idea they wouldn't react at all. Monkeys are animals while humans are intelligent, and more importantly, most of their senses are much worse. You don't smell the monkey, but that doesn't change anything about the monkey's ability to smell you - we're talking about monkeys reacting violently to humans, not the other way around.
That they'll notice a difference, sure. That they'll interpret that difference as "adult female"... far more speculative.