They tell her about the process.
Apparently, gaining the new sense is overwhelming at first, especially for their species who are used to living in deep space and receiving minimal sensory input. It usually takes several days for recipients to adjust and begin learning to manipulate their field. Gaining the psychic field did not automatically grant the ability to fight the compulsions, but it did make the individual aware of them immediately. This is not true of all owners of a psychic field, natives of this universe generally have learned to tune it out. But, if someone is acquiring a psychic field for the first time, they become immediately aware of their mind in a way they weren't before, which makes outside interference extremely obvious.
It generally took about a year on average for the soldiers to learn to throw off the existing compulsions and learn to immediately repel any new ones. Some soldiers learned to do it within a matter of days, while there were a rare few who were never able to successfully do it on their own and required outside help to free themselves.