Dreams about loved ones, especially children, can evoke strong emotions and often reflect our feelings and concerns about them. In your dream, your adult child being locked in a box may symbolize feelings of confinement or restriction. Since you mentioned that this was her voluntary choice as a spiritual practice, it could suggest that she is exploring her own identity or personal growth in a way that may feel isolating to you.

The fact that she is stacked at the bottom of two other boxes could indicate that you perceive her choices as being overshadowed or influenced by external pressures or expectations. It may also reflect a concern about her well-being or the depths of her personal journey.

Consider how you feel about her choices in your waking life. This dream may be urging you to reflect on your relationship with her and to support her in her endeavors, even if they seem unconventional or challenging. It's also a reminder to communicate openly with her about your feelings and concerns.

Overall, this dream could be an invitation to explore themes of autonomy, spiritual exploration, and the dynamics of your relationship.