"She has her shirts."
Translation:Elle a ses chemises.
No, that has no relation to the verb conjugation.
"ces" is a demonstrative adjective: ce, cet (masc. + verb starting with a vowel or non-aspired H), cette (fem.), ces (plural fem and masc) - all are used to show something/someone mean this/that/these/those
"ses" is a possessive adjective: mon, ma, mes, ton, ta, tes, son, sa, ses, notre, nos, votre, vos, leur, leurs. They indicate that something belongs to someone : my, your, his, her, our, their.
The 3rd person singular, possessive adjectives agree in gender and number with the noun they modify.
"Chemises" is feminine plural: Ses chemises = his/her/its shirts
"Pomme" is feminine singular: Sa pomme = his/her/its apple
"Chien" is masculine singular: Son chien = his/her/its dog
"Pantalons" is masculine plural: Ses pantalons = his/her/its pants/trousers