T.S.
Listen to her fears. Use the statement: "Tell me..." to discover what her fears are. For example, "Tell me what will happen when you miss mommy." "Tell me what will happen when you are at grandma's house." Then just listen, don't try and fix it or change her story into your story. Let her have her story.
Then you play the "If, then..." You ask her "If (insert her story), then what?" Allow her to follow the story to the next thing that she thinks will happen. At this point you can help her a little by asking what she would do next. For example, "If I go to grandma's I will miss you." "What would you do when you miss me?" "I could call you." Let her come up with the solutions. What you are tring to encourage her to do is understand what resources she has and how to use them.
Help her to have resources: how to use the phone, favorite blanket or stuffed animal, space to feel her feelings, permission to have her feelings, knowing how to call 911 and when to call, how she could use things like her imagination to come up with creative solutions, etc.
When she gets upset and starts crying let her cry it out and simply be there to hold her. Wait till her emotions settle naturally before you step in to support her in finding a solution to her fear. If you step in too soon you are teaching her to stuff her emotions and that her feelings aren't okay. Instead, you just let her have them and then discuss the situation afterwards.