Whether it is legal to marry a relative can vary depending on where you live. In some cultures, it can be looked down upon for cousins to marry cousins. Many have rules and laws against incest close relatives marrying one another. This is rooted in genetic concerns: close relatives who marry one another are more likely to have children with diseases or other issues. First cousins are considered to be close relatives while second cousins are not.
Cousin marriage in Islam is a marriage to a person who shares a fairly recent ancestor within a few generations. In some communities cousin marriages are encouraged and in others they are stigmatized. Cousin marriages are illegal and prohibited in some countries. Due to the actions of Prophet Muhammad and the Rightly-Guided Caliphs, marriage between cousins is explicitly allowed and even encouraged in Islam. The Qur'an itself does not discourage or forbid this practice in any way.
Grandparent, added to MsDora's profile of teacher and counselor after she became a senior citizen, gives her a new interest to explore. For those who need clarification, here are a few explanations on the cousin relationship. You do not have to memorize them in order to understand the rest of the article.