Final answer:
Jenna's mother cannot physically send her birthday presents from the grave. The most plausible option is through a trusted friend or family member who may have access to any gifts Jenna's mother left behind before her passing.
Step-by-step explanation:
Jenna's mother cannot physically send her birthday presents from the grave, as this question seems to be asking about a supernatural or fictional scenario. Therefore, options 1) through a magical portal and 2) through a courier service are not possible in reality. The most plausible option is 3) through a trusted friend or family member who may have access to any gifts Jenna's mother left behind before her passing. This could include items that were purchased or prepared in advance, or sentimental belongings that were specifically intended for Jenna.