It is entirely normal and understandable to feel a strong emotional attachment to objects that remind you of your loved ones, especially when they are away for an extended period. In your case, not wanting to wash your daughter's pillow because it smells like her is a manifestation of that emotional connection and longing for her presence.
Scent is a powerful trigger for memories and emotions, and it's not uncommon for people to find comfort in familiar smells associated with loved ones. Holding onto her pillow might provide you with a sense of closeness and comfort during the time she is away.
It's important to recognize that missing a loved one, especially a child, can evoke a range of emotions, and each person copes with these feelings differently. If keeping her pillow unwashed brings you solace and helps you manage your emotions, there's nothing wrong with that.
When your daughter returns for Christmas, it might be a heartwarming moment to share with her how you kept her pillow as a reminder of her and how much you missed her during her absence.
Remember that feelings of missing someone and longing for their presence are natural and human. If you find the emotions overwhelming or need additional support during the time she's away, consider talking to friends, family members, or a professional counselor who can provide a listening ear and help you navigate through these emotions.