On the subject of what is called singular they (Everyone has their off-days) Mittins et al. write that Jane Austen “uniformly employs this usage”. The authors refer to S.A. Leonard’s Doctrine of Correctness in English Usage (1929) here, where we may read:
probably quite as many cases of reference of they and their to words like person and one and everybody could be discovered in an equal number of pages of Jane Austen or Walter Scott and of Addison and Swift (p. 225).
Leonard continues: “there is good evidence that British usage is still about equally unfettered in the manner”.
Jane Austen does indeed make use of singular they in her letters, and a good example is:
- If anybody wants anything in Town, they must send their Commissions to Frank.
Most other examples I found occur with everybody, as in “Everybody sends their Love”. Everybody, however, has plural reference, and they or their would not be inappropriate. The case of anybody is therefore different, but it was the only instance in the letters. Usage by Jane Austen cannot therfore be considered as uniformly favourable to the construction as Mittins et al. or Leonard suggest. Another interesting point about ”Everybody sends their Love” is that the finite is not plural. No wonder grammarians and wirters on usage have problems with the use of singular they.
On a webpage called Everyone loves their Jane Austen, the author, Henry Churchyard, lists 75 instances of singular their in Jane Austen’s writings: again, not quite as many as Mittins et al. or Leonard seem to think. For all that, thanks to the author of the page for this meticulous work.