I have spent many hours researching potential candidates. The Peck family seemed to offer an excellent answer ... however, I was bothered by the fact that none of the potential women had a son. The photo album clearly shows that the mystery woman and her husband had a son. The album only covers him from the ages of 0 to about 4.
So I decided to look into the tenant of Howbury Hall after the Peck family - Major James Edward Platt (1857-1928).
The first three images are all photographs from my album. The third image is from a biographical sketch of Major Platt.
http://www.stanwardine.com/genepic/Major_James_Edward_Platt_biography.pdfMajor Platt was divorced in 1900, and married an Italian woman named Elise Castelli (b.1876) in early 1901 before moving to Howbury Hall. Like the Robert Peck, Major Platt was an avid horsing man, as well as being a very keen huntsman and polo player.
I have been unable to find the couple on the 1911 census (which might confirm whether they had a son), but they show up together at Howbury Hall on the 1901 census. Indeed after 1901 I have so far been unable to locate any information regarding Elise.
Here is a portrait I found of Major Platt's mother on Ancestry, and a lady who appears on the wedding photo.
Comparing photos is not one of my strong points, so I do not know if the photos match or not?