5yr old with severe constipation! Help!

Okay, I'll try to explain this best I can.
Laura turned 5 this yr. She has always had irregular bowel movements since birth. Tried lots of diffrent things along the way and the best that we could ever get was 1-2 times a week. Well every once in awhile it will take up to two weeks for her to have a BM. But this last time it has been 28 days,and we are worried!!!! what can we try. By the way took her to the doc and he said mineral enama's for three days and something called colfalax. (We don't like to take lab created laxitives.) We already tried Formula #3 if she takes more than 3/4 tsp she throws it up, and hasn't been as effective as we would like. The enama's also haven't been very helpfull. can't seen to get anything in....like i'm hitting a brick wall. but none the less we treid with just a little. she held it for 20 mins. Then tried again to see if we had loosened anything up and again like hitting a brick wall. A good friend recommended 1 tbsp of olive oil in a little OJ on empty stomach. So I tried it. the next afternoon she had a good size BM not overwhelming hard but fairly hard. So I tried it again. Nothing!!! So I tried one more time and sure enough she had another BM good size and not hard but well formed.
What else can we do to help. As this has always been an issue I know it will take some time to correct this problem she has but where do we start?. Are there any herbal enama's that we should try? By the way she does drink water apple juice and prune juice on a regular basis. We don't eat alot of animal products. Any suggestions will be greatly appreciated.