My first thought is that she may have problems with your Extraversion preference. Because Extraverts often talk more, especially those with Extraverted Feeling dominant preferences (EFJs), because that is the primary way they relate to people. It is my experience that they (EFJs) don’t use email as much as the phone is because they prefer direct communication. My guess is that as an Introvert, your sister prefers to reflect first before responding so that email and social media are more useful.
As to the issue of making you the problem, the E/I difference in your Type may also provide the answer. ISFJ’s usually have a pattern of staying under the radar and not making waves. They can be super achievers or have problems but keep it “close to the chest.” ESFJ’s achievements and problems can be very evident because they have a preference for processing things out loud, often referred to as “thinking out loud.”
It also may be related to the human behavior of making you the problem rather than dealing with her own issues. For both your types, your preference for Extraverted Feeling (Fe=FJ) gives you skills for paying attention to the needs of other people and being able to help people with those needs. However, in order to take care of other people, it is necessary to take care of yourself first. If you are taking care to meet your own needs, your ability to take care of others will improve.