What is the ruling on fearing marriage before one's older sister, out of concern for hurting her feelings, especially since she is not yet married and was the one who raised [me/us]?

The Prophet, peace and blessings be upon him, advised young people to marry to protect themselves. The questioner's concern for her sister's feelings is commendable, but sacrificing marriage opportunities for the sister's sake is not acceptable. Neither she nor her sister will benefit from delaying marriage and letting time pass.

If the matter were limited to a single suitor or limited expenses, prioritizing the older sister would be understandable. However, in this case, the questioner should not reject Allah's provision and lose her opportunity because her sister has not yet found her destiny. This is an exaggeration of submission to customs or an irrational consideration of feelings.

It is advisable to accept the first suitable marriage opportunity that will safeguard her chastity and fulfill the objectives of Islamic law. Perhaps this will be a blessing and an opening for her sister.

Quoting Sheikh Ibn Uthaymeen, people regarding the marriage of a younger daughter before an older one fall into three categories: 1. Those who do not marry the younger before the older, viewing it as a flaw, which is an error. 2. Those who marry the younger before the older, which is a transgression. 3. Those who fear Allah and marry whoever receives a proposal, whether she is the younger or the older. This is the one who has fulfilled the trust, for "whoever fears Allah, He will make for him ease in his affair."

Guardians should fear Allah and not prevent competent suitors from marrying those whom Allah has placed under their guardianship.