In a 2012 article for Premier Guitar Magazine, she describes the process of creating your own exercises and demonstrates how they can help with ear training, technique, getting your fingers to move in new ways, and developing a personal style of playing. For example, you could play a scale in all 12 keys in the same position on the guitar, starting in the key of C and going through the cycle of fourths.
By staying in one place on the neck you can't just repeat the same pattern over and over again - with each new key you have to move up a fourth or down a fifth to stay in position. (FYI: this works for mandolin or guitar).
To add another level of complexity to this exercise, she plays each scale descending, starting on the 2nd note of the scale, which makes it a 7-note scale. Playing the seven notes scales as a steady stream of 16th notes creates rhythmic displacement that threw me for a loop when I tried it! (B - A - G - F- E - D - C - E / D - C - Bb - A - G - F - A - G / F - Eb - D - C - Bb - D - C - B and so on...I think!). This is shown in Fig. 4 of her magazine article.
For a further level of variation, she makes it a nine note ascending scale by incorporating open strings before the first and second notes of each scale. This creates a nine note pattern which you still play in a steady stream of 16th notes. See Fig. 5 in the Premier Guitar lesson for the tab to this and good luck trying it!
Mary says that once you get the hang of this the variations are endless. You could arpeggiate the scale, you could start on a note other than the root, you could alternate ascending and descending, you could slide into the third note of each scale, you could double up or triple up on each note.
In this video for Jazz at Lincoln Center she further discusses the topic of writing your own exercises.
You can basically take anything you're learning or working on and create your own exercises to better absorb it - ideas that come from you.