fresh is good, start off with just enough to coat the food and see how she reacts, you could also offer her about 1/8 a cup of juice alone (as a drink) and see if shell take it. some dogs dont like the taste (whihc is when mixing it with the kibble will help. but she can have as much as half a cup a day of crushed pineapple, or pineapple juice.
canned pumkin also aparently has had good results.
they may not work for you, id say using natural food as an addative works in about 50% of the cases, but it might be worth a try before you go shelling out extra money on the chemical product. which aparently has the same chances of working
(pumkin also is good when youve got a dog with a loose digestive system as it tends to help with the binding)