As a coach we are not qualifed to make medical diagnosis, as tempting as it may be even when we think we know what the problem is. Loose ankle would suggest as Hammy said a weak, or sublaxated ligaments, or possible absent or torn.
Alternatively and most likely this coach mean a weak, wobbly ankle. This is counteracted by doing regular strenghtening and proprioceptive exercises.
Exercise 1- Toe Raises as hammy descrbibed with the different foot possitions
Exercise 2- Toe raises while keeping the knees bent
Exercise 3- Inversion and Eversion against resistance (Link Removed). Therabands are perfect for this, and most gym have them.
Exercise 4- Bend rise lower exercise (Start standing close to beam, 2 fingers on beam for balance. Bend your knees till about 45deg, the lock the ankles out so that you are on the ball of your foot with your heel as high up of the floor as you can. The knees should be above the ankle not infront. Then raise now standup (stretch) and push up straight up without! the knees moving just stand up so you are standing straight up on the balls of your feet. Important thing here is that as you begin to stand up your heel should not drop down. You have to keep it up.. This is a great!! exercise
Exercise 5- Wooble board balance (Link Removed). Start with two feet and progress to 1 footed stance. 1min at a time 3-4 times.
Exercise 6-Toe drags - Standing on the floor, just with your toes try and drag yourself across the floor. Bruttal but great.
Exercise 7- Balance on toes and on flat feet with eyes closed again 1min 3-4 times per stance postion.
You dont have to do all these exercise but pick 2-3 and do them regularly (well your daughter)