Charles Ellicott Commentary Leviticus 21:3

"and for his sister a virgin, that is near unto him, that hath had no husband; for her may he defile himself." — Leviticus 21:3 (ASV)

And for his sister a virgin, that is nigh unto him —This refers to his unmarried sister who, having no husband, continues in a primary familial bond with him. The next clause explains this in more detail.

Which hath had no husband —When she marries, she becomes part of her husband's household and is no longer considered as near to her brother in this regard. The responsibility for her funeral rites then falls to her husband.

For her may he be defiled —According to the administrators of the Law during the Second Temple period, the priest was not only permitted to contract defilement by attending to the funeral rites for these seven relatives, but was, in fact, obligated to do so.