The September 18 outage, which lasted almost 14 hours, affected hundreds of calls in four states and territories, and has been linked to two deaths as a result of emergency calls failing to connect.
Ms Kelly, a former Westpac Bank chief executive, is a non-executive director at Optus's parent company Singtel.
She is understood to be facing the public hearing at Parliament House in Canberra on Thursday in person after not attending the last hearing as requested because she was overseas and unavailable.
John Arthur, who has sat on the Singtel Board since January 2022, is also expected to give evidence at the inquiry.
Greens senator Sarah Hanson-Young, who has spearheaded the investigation into the outage, has previously welcomed the participation of the Australian-based representatives in the parliamentary probe.
At the previous hearing, Optus boss Stephen Rue admitted a "culture of carelessness" had existed in the lead up to the outage.
He also confirmed the telco was preparing to cut up to 300 jobs.
Kerry Schott, who completed an independent review into the deadly incident, handed down 21 recommendations and described the failings as "inexcusable".
The Australian Communications and Media Authority will also front the inquiry.
In a submission, the authority said it had completed four investigations that resulted in enforcement actions for triple-zero compliance issues in the 2024/25 financial year.
These include an Optus outage in November 2023 which resulted in paid penalties totalling more than $12 million following an investigation of the "significant network outage that disrupted access to triple-zero".
Telstra also paid penalties of more than $3 million following a March 2024 disruption at triple-zero call centres.
Singtel was contacted for comment.
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