First, I realise it's a fuzzy borderline, but I've never heard anyone put the date of the medieval/modern divide anything like so late. (The Battle of Bosworth was good enough in my day.) Does she really class Shakespeare as a medieval writer? Is this idea in common currency?
But also, the transition from Commonwealth to monarchy was in many ways a regression back into the Middle Ages, from what had in its beginnings at least been a proto-modern state, with a modern idea of human rights and politics (just read the birthpangs of English democracy in the Putney debates, and see how modern they sound compared with anything that happened for 100 years afterwards). Not only is the whole idea of monarchy thoroughly mediaeval in itself, but Charles's government set the clock back in totally senseless, spiteful ways, just because they wanted to wipe the deeds of the Commonwealth from history. They re-introduced Rotten Boroughs, for goodness' sake!
Of course, in many ways the tide of modernity flowed on under Charles and his successors: how could it not? He wasn't the absolutist his father had been (but then, he was smart enough to realise that wasn't an option). The Royal Society was set up in 1660, with him as patron - but that was simply the continuation by other means of what people like Hooke, Petty, Boyle and Wren had been doing through the 1650s at Gresham College and at Wadham College, Oxford (the latter under the Mastership of John Wilkins, Cromwell's brother-in-law). If the Restoration is going to be given credit for that, then by the same token we might as well blame it for the Fire of London and the plague - a nasty, mediaeval disease, don't you know.