Poor little dear, she's in a vicious cycle, she knows it hurts to poop, so she holds it, which makes it hard to go and confirms her fears :(
Milk is constipating, try giving her Activia yogurt instead of milk. Increase her water drinking, i see you are giving her the gummy fibers, i used them with my guy, but unless she is drinking lots of water the fiber cannot work properly, the poop gets hard to pass, she also may need more than one gummy a day.
Bananas are constipating, give her apples with the skin on, or applesauce, prunes, no processed foods or foods with lots of sugar, added or natural. Make her smoothies (some Activia, fruit, some fruit/veggie juice and ice) to encourage and get her to eat something that will help her body. Oatmeal, sliced grapes, whole grained cereals and breads, and broccoli (raw with some ranch dip, my guy calls them "little trees") are also good fiber food choices.
Make sure she is getting plenty of physical exercise, running and jumping helps to keep things moving through her intestinal tract. Have her kick around a soccer ball and chase after it, play hopscotch, jump rope, whatever gets her moving.
And set aside regular times for her to sit and try to poop a few times a day, don't wait for her to say she needs to go. Give her some fruit and water a little before, let her have a book she reads just a those times, "It Hurts When I Poop" is a good one.
http://www.amazon.com/Hurts-Story-Children-Scared-Potty/d...