Protect the camp
In the manual for the breathing technique she practiced, it said that if one saw only herself in the mental image while reciting the mantra, then they would be able to cultivate alone without a need for a partner or any form of external influences to interfere.
But if on the off chance or by accident, there is a second person in the mental image, then the practitioner would have no choice but to dual cultivate with the person that appeared in their mental image.
This would allow them to maintain a balance in their inner self and then to achieve a better cultivation speed and result with the breathing technique.
The Idea of dual cultivating with Nathan caused Elena to blush slightly due to being embarrassed by the thought of doing something so intimate with Nathan thus she hadn't brought it up since the mental image sprang up in her mind even though she had decided to keep on using it despite it's halved results.