What is the ruling on one who was unable to attend their mother's burial due to being abroad and straitened circumstances?

May Allah عز وجل improve your solace regarding your mother. The general rule is the obligation to obey one's parents in what is good. However, this is restricted to what benefits them and does not harm the child. If there is no need for your visit, or if harm would befall you, then there is no blame upon you for not complying with her command. We advise you to show piety towards her after her death by supplicating for her forgiveness and mercy.