Holm was debuting in the UFC when she beat Pennington by decision.
The 38-year-old has been afforded three title shots since she lost the bantamweight belt to Miesha Tate in 2016.
Despite her struggles to beat the likes of Amanda Nunes, Cris Cyborg and Germaine de Randamie, she still has a title in her sights.
"If I wasn't still trying to climb and fight for that belt, then what would I be doing this sport for anyway?"
She has lost to each of the last three champions that she has fought with losses against Holm (twice), de Randamie and Nunes.