It is horrifying to witness such unbecoming acts by these nuns. As Dolce Vita said: even lay people define the acts of spitting and destroying property as poor behavior. To have ordained individuals perform such acts reflects very poorly on the 3 jewels.
Well, damage has been done as this event occurred 15 years ago. So, as Dharma practitioners, we need to use this "bad" situation as a "good" reminder of what we should never do. These nuns' behavior on this occasion is a lesson for us to develop an understanding on why people cause such damaging results with their actions: why did they do such a thing?
It must be out of fear. Fear stems from ignorance. Perhaps, these nuns acted this way as they were ignorant of the truth about Dorje Shugden.
Based on this result, we can learn that we should not act out of fear because, in doing so, we almost always create consequences that is damaging to others and ourselves. In Dharma, we are taught to act out of love to benefit others. If the nuns had acted out of love, they may be able to uphold their respect for the Dalai Lama and fulfill HH’s request while also keeping their vows to treat ALL sentient beings from all 6 realms with kindness (assuming they truly believe that Dorje Shugden was a spirit at that time). Example: As written by Galen, donate the Buddha image to another monastery etc. By acting out of love, we will, at the very least, not cause harm.
Similarly, we should not act in ignorance. Before taking action, we should develop understanding because as Dr Brian Weiss (a doctor and author on regression hypnosis) puts it understanding dissolves fear and develop love.
Despite the damage that is done, we can still somewhat salvage the situation by taking the lessons to be learnt from this sad situation. There is a silver lining in every cloud, may our study of Dharma empower us to also search for and find this lining.