Worked on Steven Mack, Lucy's older brother and probably the most successful of her immediate generation, today.
There are some websites that offer overviews and cobbled together biographies, e.g. one on family search or one on gensearch.
But the majority of these are dependant on the 1853 memoirs of Lucy Smith Mack, printed by Orson Pratt in England, and two histories of Oakland County, Michigan, one by Durant from 1877, and one by Seeley from 1912 (in two volumes). This is esp. true for the gensearch article, which is an excerpt from Durant.
Since Major or Colonel Stephen Mack was busy in Detroit as well, esp. during the War of 1812, he might be found in a history of Detroit also.
If it is important to distinguish what Lucy knew when about her brother: there are important differences between the rough draft manuscript history dictated 1844-1845, and the manuscript history in its clean copy given to Lucy by her "stenographers" in 1845. Specifically, Horace Stanly's letter was added, which contains details and dates that are not in the draft and may thus indicate information that Lucy was not aware of.