Isles, apologies, completely missed your reply on the details of the 1871 marriage

With that information and that 1901 census entry, this looks like Ann with children in 1881 - likely father off to sea I would imagine:
Ann Lownie 35, Seaman'S Wife, b. Glasgow
William Lownie 11
James Lownie 8
Charles Lownie 2
Address: 3 St Matthew St., Dundee
And the 1901 entry:
Robert Lownie 58, AB seaman
William Lownie 28, bookbinder
James Lownie 23, Sawmill Labourer
John Lownie 17, Linen Calender Hand
Address: 7 St Matthew St., Dundee
Monica
