It's interesting to see how the answers contrast.
Ne-Monster (Fi):
Focuses on how the behavior makes her personally feel. She assumes she correctly empathizes (which she might! we lack all the info), and then figures out what she would do in her friend's shoes. Since her behavior doesn't match her friend's, she grows annoyed.
Heart (Fi):
Having experienced similar problems, immediately empathizes with the ISFJ friend as she's been through something similar. She too may or may not be correct. Knowing what her own needs were, and what others did that helped and hurt her, constructs a course of action that she views as helpful.
Proteanmix (Fe):
Pays attention to what the person is expressing, but remains unsure of what the motivations are. Avoids making assumptions, and instead develops a test that will help her better interpret the situation. This is what some people can see as manipulative, because she's putting the friend in a situation where the ISFJ can return the favor or do nothing. Based on that, she will have the answer she seeks, and react accordingly.
Synarch and onemoretime (Tert Fe):
Simple. When a person complains, they seek sympathy, so give it to them. (There's no need or reason to see deeper into it at this point.)