So far I find no child Elizabeth of any of Andrew's siblings, but a strong hint in the 1911 census is John H(ouston?) Sherrard (40), a draper, of 1 Lisburn Road, St George's. Elizabeth Sherrard (40) is John's wife. They are 13 years married; daughter Catherine L(yle?) Sherrard; son Andrew H(ill?) Sherrard.
I think Catherine Lyle (younger sister of Andrew Hill's wife Janet) married Samuel Morrow; and their daughter Elizabeth - Andrew's "niece" in informal usage - married John Sherrard. This fits but needs some checking in Carnmoney records (and I'm not local). And it may not answer the original question - sorry if I've wandered from it.