Thanks for the update, Mr Red.

I take back what I said about:

"The "r" in 'Libera' looks like it might have been squeezed in as a correction as well."

I thought there was a shadow of an "r" after the "b" but I just had a bit of a playaround with a graphics programme, adjusting the dark/light, contrast, etc and it appears to be a blob of colour in the stone itself, so ignore that bit.

I vote for "Libera nos Domine".

Regarding the opinion that the style/font was too Georgian/Victorian for 17th C, it would be worth looking at other inscriptions from the time of the plague inscription to see if that font was used. I think the font is similar to a lot of printed works of the time and also possibly fonts used in church inscriptions - no, not fonts for christenings! LOL

I still stand by my hypothesis that the inscription was not necessarily done by a literate or skilled stonemason given the loss of lives during the plague.