I think she was very passionate about what she did and that's what put her in that position at HMV. And the very fact that HMV put an intern in charge of social media highlights their disregard for online - which overall was responsible for their demise anyway.
I think her actions were a culmination of her passion and frustration. Frustration that has probably been felt by many of her colleagues too - long before the company went under. It's not like online has just snuck up on them.
Belbin's team role suggest that for an individual's strength, there is an 'allowable weakness' on the flip side. Poppy's strength appears to be her passion for what she does. Her allowable weakness is her outspokenness for said passion. HMV benefitted from her passion...and should have had a contingency plan for her weakness.
Whilst I appreciate wariness of her actions, if the circumstances of HMV were different, she would have been hailed a genius covertly. Look how it trended. Their social signals will be going through the roof. Negative or not, most of us have experienced Google's inability to yet distinguish sentiment for affecting SERPS. Kind of like a female UK Ryan Holiday - whose book is a great read, by the way :-)