Dreams involving deceased loved ones often carry deep emotional significance, especially when they are rooted in unresolved feelings or a desire for connection. In your dream, the appearance of your mother, who is cremated, suggests a longing for reconciliation or a need to process your grief. The fact that you initially recognized her as your aunt but then confirmed it was your mom indicates a struggle between acceptance and the desire for her presence.

Your interaction, where you both express sorrow, points to underlying feelings of guilt or regret. It’s common to have such emotions when we lose someone close. Your mother's reassurance that there is "nothing to be sorry about" illustrates a comforting presence and the desire for healing. This part of the dream may symbolize your need for closure or forgiveness, both for yourself and from her.

The mention of wanting to introduce her to Cassius, and her excitement, suggests that you are looking to share aspects of your life with her, reflecting your wish to maintain a connection despite her absence. The little whiteboard and the mention of a white horse might represent communication and purity, indicating that there are unspoken thoughts or feelings that you wish to convey or explore.

Overall, this dream could serve as an important emotional release for you, allowing you to confront your feelings toward your mother and recognize your ongoing connection to her. It might be beneficial to reflect on these emotions further, perhaps through journaling or talking with someone who can help you process your thoughts about your mom and your feelings of loss.