To everyone who is worried about the guy snapping her: How many guys have successfully stolen someone’s girl, or slept with her, by spamming her repeatedly on social media without any response from her? I’m not worried about that guy at all.
Girls are anti-confrontational. To them, blocking is a confrontation. Most women will just ignore a guy they aren't interested in - not read the messages and/or not respond to the messages. In OP's case, his girl isn't even opening the messages. I don't see how this is some big deal. Guys can snap anyone they want. What if a girl snapped OP and he didn't open it or respond? Is that automatically his fault and means he's about to bang her and his girl should be really worried?
As far as why does she have snapchat, because people use it to communicate. It's social media. That's like saying, "Why do you have Facebook or Instagram or
text-messaging if you are in a relationship?"