In my country, talking from the legal aspect, parents don't have many choices if any at all. The thing is that by our law parents are obligated to vaccinate the children and if they don't they can get penalized (from money fine, a jail sentence up to that children could be taken away from the parents and family by social service). That's the ugly side.

From a bit brighter side, luckily any pediatrician (or at least most of them) do not stick blindly to this legislative, leaving the parents a choice to refuse the vaccination without reporting them to the authorities. Although, some might make severe pressure or even throw threats toward parents.

There is also a big movement against current laws in this regard. Associations formed around the cause (as some others too) protest loudly demanding to abolish the law and giving parents at least the opportunity to choose if they want or not to vaccinate their child without being threatened with above-mentioned possible repercussions.

A few days ago a big protest in this regard had been held. It was nice to see a lady, who is a medical doctor otherwise, leading the protest explaining possible consequences through her own case and admitting how blind she was until it happened to her child. That raises the hope for a possible sooner change.

However, in this particular case of your niece, I don't think it's connected with vaccination. As first the girl was vaccinated 2 months ago. If that's something directly connected with it, it would show up earlier. The only impact that this past vaccination might have in this particular situation is lowering her overall immune system for fighting against the current disease.

All of that, even more, because of the Dengue is a viral disease which incubation period is (2-10 days) way shorter than 2 months in the first place, what would also mean that the vaccine contained the virus what is highly unlikely. The only exception is if the vaccination that she received was against the Dengue, as then of course vaccine had a small portion of the virus as otherwise, it wouldn't be the vaccination. But she could also have been bitten by infected mosquito anytime, anywhere without even noticing.

That's why (from the information you've provided) I don't think this particular case has anything to do with her previous vaccination.

I also believe while it's important that we know more about this things, have the freedom to choose not only to vaccinate or not but as well with what kind of vaccines, when, how often, etc., it's also important that we stay rational and avoid to jump to conclusions that might not have much sense.