Does 11B for the Pennsylvania Army National Guard help out in nationwide situations, like active shooters or natural disasters?

Yes. The NG is one of the first responders before the federal response.

NG can be activated for both National problems,( under Governors ok) and activated by the state for state disasters. Hell there are probably PA NG helping with the flooding goin on now.

Well, the National Guard falls under the state's jurisdiction in terms of what you're asking. Generally an active shooter is over long before the NG could even consider mobilizing, wouldn't count on that. However, for natural disasters sure, it's really up to the governor. You can also be deployed in support of overseas operations.