I wonder if a secondary motive for not seeing a career in poetry as a viable option for either Tonks or Mirrlees (or equally Laura Riding, another apostate) was the anomalous nature of being a female Modernist poet who didn't wish to conform to the inherited stereotypes foisted upon them by the literary establishment. Tonks was clearly never going to be a mainstream poet and what few notices I've found about her (written by men) do often focus somewhat belittlingly on the frisky, sensuous loucheness of her work, which is one of its great appeals and makes it so redolent of its time: how many male poets of the '60s capture the flavour of the period so well? (The Liverpool poets, for example, seem juvenile in comparison.)
For a taster of her brilliantly-titled volume Iliad of Broken Sentences try this discontinued blog.
Guardian obituary here.