“I am writing from a Chicago suburb. I am married to an American citizen for almost three years, and plan on applying for U.S. citizenship as soon as I can next year. My mother is 69 years old, back in Ireland and in good health. She is there on her own pretty much, and loves the U.S. Can my husband act as a green card sponsor for her, as I won't be able to sponsor her until I'm a citizen? We have heard this won't be possible, but is there anything he can do in the meantime for her?”
There really isn't, as U.S. immigration law doesn't provide for in-law sponsorship.
Once you become a citizen you will be able to sponsor your mother as an immediate relative, which means the processing time will be significantly shorter compared to the other family preference categories - expect the wait to be somewhere in the region of six months to a year.
You will not be able to start the sponsorship process until your citizenship case is finalized. Once that happens, you'll notice that one of the documents you'll need to complete is an affidavit of support, which confirms that you will assume any financial responsibilities should your mother fall into difficulties, such as medical, welfare, etc.
Your husband will be able to act as a co-sponsor of the affidavit, but that's about all he'll be able to do in your quest to secure status for your mother.
It's a big move to make at the age of 69. Remember to look into such issues as health insurance - so critical in the U.S. - and the transfer of any pension money she receives at home. As far as the latter, the Irish Embassy's website at www.irelandemb.org should provide useful assistance.