Q1: Why is her previous name not included in the article?
A1: Per MOS:GENDERID, and past discussions on this article talk page, Lia Thomas was not notable under her prior name, so we do not include her previous name in the article or on this talk page.

Previous discussions on this article talk page include:

Also note the Penn Men's Swimming and Diving website lists her as Lia Thomas (e.g. for 2018-2019, select 500 Free, 1000 Free, or 1650 Free), and her highlighted name links to her Swimcloud page for her entire swimming career, with no explanatory notes nor deadnaming on either website.