The commas on either side of "Griselda" are used to set off the name as an appositive. An appositive is a noun or noun phrase that renames or identifies another noun or pronoun in a sentence. In this case, the name "Griselda" is being used to provide additional information about "my older sister." The use of commas around the appositive helps to clarify or provide emphasis on the name but is not necessary for the sentence to still make sense.
You can put commas on either side of "Griselda" in the sentence "My older sister, Griselda, is going to college in the fall" to indicate nonessential or additional information. The commas set off the name "Griselda" as an interrupting phrase, providing additional details about the subject (the speaker's older sister) but not fundamentally changing the meaning of the sentence.
