Her final appointment before being raised to the episcopate was as Rector of the Benefice of Glan Ithon in the Diocese of Swansea and Brecon (2015 to 2016).

[2] In addition to her full-time ministry, Penberthy undertook part-time study in quantum physics.

[6][7] Her doctoral thesis was titled "Reading the "Paradoxical Book of Bell": a case study in theology and science".

From 1985 to 1989, served as a full-time deaconess in the Benefice of Llanishen and Lisvane on the outskirts of Cardiff and in the Diocese of Llandaff.

[9] From 1994, she was also a Provincial Officer in the Division for Parochial Development and Renewal;[2] this was an appointment focused on evangelism.

[12] On 8 September 2015, she was inducted as the Rector of Glan Ithon (a benefice consisting of Llandrindod Wells (Holy Trinity) (Old Parish Church) and Cefnllys with Diserth with Llanyre and Llanfihangel Helygen) in the Diocese of Swansea and Brecon.

[3][10] A social media post from a personal Twitter account in March 2021 which said "never, never trust a Tory" led to significant online criticism, from the public and other clergy, including from Archbishop of Canterbury, Justin Welby.

[20] From 31 August 2022, Penberthy was again off work on sick leave;[21] on 18 May 2023, she announced her retirement with effect from 31 July.

[3] In 2015, whilst serving as rector within the diocese of Bath and Wells, she stood as Labour candidate in the Blackmoor Vale ward of South Somerset District Council.