The ל.  belongs to the date, it's a truncated לפ"ק which is an abbreviation of "לפרט קטן" and indicate the "thousands" is not mentioned it the date.  A full date for this year would be התרע"א -- 
ימי שני is a biblical expression, which refers to a persons age, more less saying "the days of her life when counted in years:"
נ"ח (or slightly less probable נ"ה) is the gimatriya (letter value) of the years of her life: 58, or possibly 55.

The day in Sivan in 18, the Hebrew letters transposed to create the word חי, which means "living" or "alive"` a popular transposition.