I’m sorry but she’s in the wrong can you not see that?
Big issue with diesels from a climate perspective is the particulates, which affect climate change because they increase the amount of rainfall. Diesels were lauded as a better fuel than petrol for years because they were far more efficient and used less fossil fuels. For years the tax incentives were based on getting people to switch to diesels in terms of fuel tax, road tax etc.Petrol efficiency has since caught up so that argument doesn't hold up hence why in the last few years the attitude towards diesel fuel has changed.
Also have to ask how old is the car she's driving. If it's a slightly older one then she could be considered to be more environmentally friendly because she'd have arguably bought it when it was considered the 'greener' alternative and, up to a point, keeping the older car running will have lower emissions than from building a new car. If it's under 2-3 years old then yes it's a stupid choice to make. If it's over 10 then chances are she would be better getting a newer petrol car in terms of emissions.
Protestors don't tend to be particularly well off so the cost of electric cars is probably beyond their financial means right now. There is still the argument that although the emissions out of the arse of the car are reduced there's still massive emissions for generating and distributing the electricity to power the car. It's not solved the problem, just pushed it further up the chain (although as we move towards more renewable sources this problem is reducing). There's also the environmental issues over mining for the metals needed for the batteries, like lithium.
Everyone will seemingly be a hypocrite somewhere. Dyson and JRM banged on about Brexit for ages then moved their businesses abroad. I want to see an end to homelessness. Do I let homeless people sleep in my house? No. I want to help towards climate change but I still eat meat.
Of course we need to all look at what we can do individually but it's all chicken feed compared to governments and big business and unless they're pressured to do something about it they won't. They'll do whatever is cheapest.