She had developed something called non-cardiogenic pulmonary oedema which usually happens in response to a one-off episode of vigorous lead control or collar mishaps, or a choking episode on kibble, for example. Unfortunately, there is no specific reversal treatment and they require intensive care with oxygen therapy. Some dogs even require mechanical ventilation at specialist centres and the condition can be fatal. These events result in fluid accumulation within the lungs.
Thankfully Marron began to improve after 36 hours and made a full recovery but it serves as a reminder that excessive pressure on collars and leads, even for a few seconds, can cause serious harm. It may also be prudent to avoid large kibble dry food for young/small dogs due to the risk of choking.
Marron received round the clock monitoring in case there was deterioration. There are also no long-term concerns.