Is disclosing personal information about a friend (without mentioning her name) for the purpose of helping her, after having sworn to keep her secret, considered a betrayal of trust and a breaking of an oath, and what are the consequences of that?

The general principle is to keep people's secrets, especially if requested. However, if the secret-holder's name or anything identifying her is not mentioned, there is no harm, especially if it serves a benefit. Regarding the oath, you are required to pay its expiation if you break it by revealing the secret, unless your intention when taking the oath was to refrain from disclosing the problem and its owner without mentioning her name or anything that identifies her; in that case, you have not violated the oath. The expiation for an oath is feeding ten needy persons, or clothing them, or freeing a slave; and whoever cannot find [the means] - then fasting for three days, as Allah the Almighty says: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or freeing a slave. But whoever finds not [the means] - then a fast of three days. That is the expiation for your oaths when you have sworn. And guard your oaths. Thus does Allah make clear to you His verses that you may be grateful."