As it turns out, Gilbert's character was written out to put more focus on Leonard's relationship with Penny, which was heating up and drawing support from fans at that time.

Source: https://screenrant.com/big-bang-theory-young-sheldon-paige-replacement-leslie-winkle/

Since Sheldon and Leonard's sperm bank shenanigans took place before meeting Penny, it is not something that she was ever explicitly made aware of.

Source: https://screenrant.com/big-bang-theory-opening-scene-cut-leonard-finale/

"We are raising as much money as we can for St Leonard's Hospice whose support was invaluable."

Source: https://www.yorkpress.co.uk/news/23501929.roy-freers-family-take-runs-st-leonards-hospice/?ref=rss