“I became an American citizen last year. My husband is also American. My sister in Ireland would dearly love to come to the U.S. She has the equivalent of a high school education, is a hard worker (right now she does clerical work), and would really benefit by coming to live with us here. She is 22. She has been here a few times and always left before her 90 days were up. It annoys me when I see how long it takes siblings to sponsor siblings, yet I don't know of any other options. What can we do for her?”
There's no doubt that the family-based fourth preference categories reserved for siblings of U.S. citizens aged over 21 is impractical.
The category allocates 65,000 green cards on an annual basis, which is not nearly enough to meet demand. For the month of July, fourth preference visas are available to those who had their paperwork filed on or before May 1, 1995. It's even worse for natives of the Philippines - the processing date there is December 15, 1983!
It takes roughly 12-15 years for a fourth preference green card to be issued, which means it's impossible to make any kind of immediate plans around the category. There's a backlog there that's crying out for some serious attention, as are many other areas of U.S. immigration law - matters that will hopefully be tackled by Congress sooner rather than later.
From what you've outlined your sister isn't eligible to be sponsored for permanent residence here. Most of the employment-based green card categories require a university degree at a minimum, except for the “other workers” category that, unfortunately, is oversubscribed just like the family fourth preference.
Perhaps your sister may be eligible for a J visa as part of an exchange program. Or maybe she'd like to continue her education here and apply for a student visa.
You should speak with a qualified immigration professional to explore possible options along those ends. Also, she likely applies for the annual DV-1 diversity visa lottery, and she should continue to do so, even though the odds of success aren't very good.