Maggie Sumner was the only female artist to contribute to the first five issues of The Yellow Book, the fashionable magazine edited by Aubrey Beardsley which ran from 1894–97, taking its name from the notorious covering into which controversial French novels were placed at the time. Her pen and ink landscape sketch Plein Air appeared in number four, the last of the volumes issued under Beardsley’s editorship. Her career after this is as yet unrecorded.

A collection of papers relating to the Sumner family in the possession of the Cumbria Archive Centre includes a series of eleven (unpublished) autograph letters by John Ruskin to his promising pupil, Maggie Sumner, dating from 1881–1886, which suggests that they may have met both in Oxford and at Brantwood. Towards the end of his life Ruskin had a number of correspondence pupils. His first comment in June 1881 was that her drawings were excellent with scarcely any fault. He gave her constructive criticism as in this letter of 5 July 1881 with detailed commentary on a drawing of a photograph of Rouen:

I must not keep your drawings longer, though they still puzzle me, and not a little. With most students, the tendency to lose breadth in defining parts is a mere weakness: - in you, it is a kind of strength; the intensity with which you fasten on complex forms and colours having something in it like old German involved Gothic. Still, I must check the exaggerated - power, I will call it, rather than fault - and ask you to tell me if on seeing your copy of the Rouen Photo again with a fresh eye, it does not appear to you patchy, chippy - gritty, - hatchy, - botchy - (I don’t mean all these things - but something which they all partly describe) - as compared with the original? - Try a little bit again and see if you cannot get it softer and more like shade, where shade is, and more [broad] in light where light is. And - in trees, do a single branch instead of a whole tree. And do it perfectly or as perfectly as you can - keeping the shades mysterious.

In May 1883 he wrote:

In May 1883 he wrote: I liked your drawings much more than I told you... Work at anything you can do without too much trouble while you’re here - mossy rock if possible, and send it me.

On 6 Jun 1883 Ruskin instructed Sumner what to draw:

In the first place - attend to sky. - drawing all interesting cloud forms you can seize - and noting effects of morning and [evening]. In the second place, draw tree branches and foliage masses for light and shade only and anatomy of branch - letting colour alone. In the third place - draw any birds you can see - any here and paint any that are going to be cooked. Fish also, if to be had. I don’t think there’s any chance of your getting a scold from me, unless you stop working.

And on 15 July 1888:

Sketch the clouds in pencil - add from memory all you can, in colour the day after, if possible...The birds I meant were geese - ducks - cocks and hens... try to draw a Hen’s wing! or a duck’s breast! - I am so glad you are happier in your work - Be sure you will be more & more so. -and more useful than in any other way.

The last letter dating from 24 September 1886 praises the development in Sumner’s work:

your becoming fastidious in choice is the best possible sign. - But try to see how by a little change in place or introduction of minor object, even the imperfect subject may be made effective. I hope to be well enough to give you a scolding at Brantwood next time you are near me.