[1] McLellan was educated at Bearsden Academy[2] before going on to graduate from the Glasgow School of Art with distinction.
[1] In her third year she studied in the workshop of Charles Baillie, an artist who worked with stained glass.
[3] McLellan pioneered the use of a stained glass technique called "Dalle de verre" in Scotland.
[2] In his book A Lap of Honour (1967), the author Hugh MacDiarmid dedicated the poem The Terrible Crystal "To Sadie MacLellan (Mrs Walter Pritchard)".
In this poem MacDiarmid praises "Clear thought" and "the open and unbiased mind".