I dont think Mrs. Mary Mack had anything to do with any nursery rhyme - you will see from the information below that she had just been widowed for the second time and that was the reason she was dressed 'all in black'.
I hope it helps?
Mack, Mrs. Mary. Missing. Lived at Bitterne Park, Southampton, Hampshire. En route to - 446, West 56 Street, New York, USA. Aged 50 years. En route to daughter 446 West Street, New York City. Ticket E77.
Had been recently widowed.
Mary Mack was the daughter of George Lacy and Mary Evory, and that she was first married to John Arber, second to Edward Mack.
Insurance claim C188. Life $15,000. Property $500. Claim filed by daughter.
Body buried at Sea.
(Extract from the American Red Cross Relief booklet case no 286)
(English). An aged English woman was drowned while coming to this country, after the recent death of her husband, to make her home with her only daughter. The daughter's husband, a waiter, at the time of the disaster was recovering from a severe attack of typhoid fever. The mother's body was recovered, and this Committee provided funeral expenses. Later, it was learned that the body had been buried at sea. The mother was bringing her household goods, a large amount of clothing and some cash, the exact amount of which is unknown, and, in view of this property loss, the daughter was permitted to keep the appropriation. ($100).
MRS. Mary Mack was twice widowed. If you had checked the biography before posting you would have discovered that. If you had checked the profiles of the people you contradicted you would know that Mr. Ticehurst is the editor of the British Titanic Society's magazine, Atlantic Daily Bulletin, and a long time researcher.