A couple of useful sites, although I did a quick look and didn't find a reasonable match. If you have names of any of Margaret's siblings, it might help in the searching.
Also, if you have access to ancestry, you could try searching on her married name, and then check immigration records. If she was named as a "friend" on someone else's trip (as a cousin or aunt), you might get clues based on their originating location.
There might also be clues in the names of her children, since the Irish tended to reuse family names. Perhaps Margaret had a sister Julia (or maybe that was Albert's mom) or Alice?
btw, 1900 Census shows Margaret as being born in March 1863, not that it means anything significant.
Also, finding her marriage record might help. Do you know where in NJ the oldest son was born? That might be a reasonable place to look.