regarding the immigrant status, nothing will happen under the current administration.
Regarding the freebies, you can contact the local social services in the locality where she lives and would be applying for the TANF and food stamps, ext. . The don't take anomous tips. You'll need to provide a written statment to go to a case worker. They will not care about legal status so it is a non factor. Your statement should simply be that you do not think that all household income is being reported. and you can cite details regarding the source of the extra income (husband). At some point she will have to revalidate her benifits and at that time they can use your letter to ask her to verify the income. If she provides a good explanation then thats the end of it. The truth is you have no idea what her true financial situation is. I don't like fraud, but there isn't anything you wrote to indicate to me she might not be entitled to what she receives. There seems to be a lot of anger and knowledge of her history in your note which makes me think maybe this may actually be someone close to you , maybe a family member, or someone you have had a long feud with. I'd caution you not to do things out of anger. It has a tendancy to just bring trouble your direction. If you don't like this person, just take another direction, and let this play itself out. If she is doing something illegal, she will likely get caught without your help.