First off, her main duty is to protect ponies from their own nightmares. She will only intervene if the dreamer is in danger. So Luna can help the dreamer by protecting it, attacking the threat with her magic and give guidance so the sleeper. Despite having some control thanks to her powers, it remains the dreamer's and is mostly in control of it. However, she is full aware that she must be very careful to not affect the dreamer's psych to damage it permanently. For example leaving a mark psychologically.







Also, I'm pretty sure she've seen a lot of dreams involving her in... many pervasive ways. Or her sister. Or even both. She knows that she can't do much, since all ponies have their own deep secrets and fantasies.

