Blackmail from the liberal democrats?

This seems a bit strange. Nadine Dorries, following losing a vote in the House of Commons, has this to say on her blog:

"...the difficult situation we had been put in by the Liberal Democrats. Some obviously disagreed, but politics yesterday was certainly at its dirtiest and most complex. I would never have thought that the Liberal Democrats would have applied so much pressure..."

The BBC sheds some light on what this dirty politics might be:

"[Dorries] blamed Deputy PM Nick Clegg for Mr Cameron's coolness towards her amendment - claiming he had "blackmailed" the prime minister by saying that Lib Dem MPs would not vote for the health bill if her amendment was carried."

So, the Liberal Democrats are against a proposed amendment to a bill to the extent that they're willing to (or threaten to) vote against the bill if the amendment is included. Whether you agree with them or not, this would seem to be a case of standing up for their principles. Perhaps Dorries complaint is that this, if it occurred, wasn't done publicly enough? (Though one would have thought it obvious that the LD would be against it). Either way, if this is dirty politics can we have more of it please? Consistent backing of principles in politics gets my vote.