Have you actually contacted the Cemetery.
She may be buried there but without a headstone.
but then found this
Address: Ed Leblanc Ln, Fredericton Junction, NB E5L 1W3
This cemetery is adjacent to the
Hermitage Cemetery (Catholic)
Some graves were moved from their original location here to the Fredericton Rural Cemetery Extension farther down Woodstock Road.
Gladstone Cemetery, Fredericton Junction
although I don't see her name there but there are both Alexanders and Boones there.
Wilmot Rural Cemetery
395 Woodstock Rd, Fredericton, NB E3B 2H9
in 1921 Mariah is living at Baushey Brighton, Victoria and Carleton District, NB with her son George