I don't know about her capacity for empathy. I think it is something she struggles with. I think when people get upset in front of her it's hard for her, not necessarily because it makes her feel sad, but just because she doesn't know how to react. The video she put up entitled "Amma crying" or something is a good example of this, although some people read it differently. This is just my perception of her. I do read her as a deeply insecure person who might be prone to manipulation because getting people to do things for her validates her.
I do think there are a lot of vloggers including cancer vloggers who have narcissistic tendencies. It often does take a particular type of person to want to share their life with the world and a lot of these people end up becoming vloggers. I'll probably get shot down for saying this, but I personally think Peeweetoms was a lot like this...in a lot of ways more than Tiffany. His relationship with his wife bore more red flags than Tiffany's to Matt's. I don't wish to speak ill of him, but that was highly apparent when I watched his videos, and I'm not sure he faced the same criticism...perhaps because he was a white male.
One thing I would say is that if her being this way is a result of her relationship with her Dad, I don't necessarily blame her. It isn't the fault of little girls or grown women that there are so many men who desert their families. Their trauma shouldn't become a sick societal joke. It shows real ingrained sexism I think when we start blaming their actions on their "daddy issues", like they are the problem and not their subpar fathers. What I do have an issue with is with things she does as an adult that have negative consequences on others.