Finding a good therapist (one you click with) can take time. I would suggest writing out a list of questions to ask a potential t (yeah, that stands for therapist or therapy depending on context). Figure out what you want to get from therapy (support, problem solving, help with boundaries, etc?) and find out over the phone how the therapist responds to those questions. Is also good to ask what they generally work with (ie: mostly depression? Eating disorders? Families? Couples? Trauma?...) and then what their theoretical background is (do they do mostly behaviorally-slanted therapies? Psychodynamic? Person-centered? Etc). I personally prefer a therapist who is more flexible with their approach and combines their skill-sets to best help the individual client, but you may want someone that is skilled in family systems therapy if you want to address the stuff with your sister.
It can take a while, and you may see a t for a few sessions then decide they are not the right t for you.