More information will really be helpful. If I understand right, you are looking for someone named Nell, whose maiden was either Dillion or Johnson.
Do you have any idea when this Nell was born? Have you looked for her birth at http://www.freebmd.org.uk/ ?
How do you know of her existance - from census records, or family story? Did she marry in England or the US?

It is going to be really hard to find her without that info- her birth name could have been Nell, or Ellen, or Helen, etc.

Does this match her at all?
https://familysearch.org/pal:/MM9.1.1/XCWN-M43