It has happened to me of course. I surelly find adult people harder to pick out a new language comparing them to the younger ones.
My strategy is to leave them homework to do during the days/hours they�re not going to see me.
For instance, once I did something very motivating and different ( its what they told me). The activity was called, " people I love". They had to dedicate a whole page of a notebook for a special person (someone they love: mother, father, son, daughter, pet, etc) one per day. They needed to spend a little more time than usual with them and write down about their physical appearance, likes, dislikes, professions, hobbies, etc.
I can also choose some other activities every week such as:
keeping a diary record--simple past
Planner-future
Self reading project...etc.
I know it can be frustrating and I congratulate the worry you have for your students. But don�t desperate just try first of all to make a needs-analysis (see where is the unmotivation coming from and what she needs the English for) and then prepare extra activities for her so she does not miss you- its how I tell my students the reason I make them use English at home when Im not there jjeje.
* Another thing, your feedback may be lacking of something as well. For me; lesson taugh, lesson evaluated at the end of the class and lesson recalled at the beggining of every next class*
I hope my little teching experience helpt you in something.
