Let's start from the top!
Around her neck is a necklace of golden marigold flowers. In Mexico these marigolds, known around the world as Mexican Marigolds, are called flor de muertos, which translates as flower (flor) of the (de) dead (muertos).
On Dia De Los Muertos, or Day (dia) of the (de los) Dead (muertos) families in Mexico (and other countries) decorate altars to honor, remember and celebrate the souls of their dead relatives.
The dazzling flowers remind Skelita and other souls of the sun. In fact, they are so bright that it is said the flowers can guide souls back home. Families use hundreds of marigolds to invite souls home to celebrate dia de los muertos. Some people even use the golden petals to make a path to the altar for souls to follow.
Since Skelita is already a soul herself, why would she need her own garland? Well, as we learned in Scare-itage, the necklace was a gift from her grandmother and is a symbol of family love. Also, I bet the marigolds remind her of the sunny skies of Hexico while she is away at Monster High.