What to give a constipated child ?

I have a 6 yr grand daughter that has been constipated off and on for the past 2 weeks. Her mother has tried an oral laxative on several occasions with some results, but this past few days she has been very constipated and she has been spending the week with me. She is out of school for the summer and will be with me most of the time. I tried a suppository this morning, but no result. I just happen to be searching through my bathroom pantry and happen to come across an old fashion child's enema bulb syringe. I had used it a number of times on my children when they were younger and was wondering if I could use this and maybe try placing her over my lap in the bathroom and give her an enema with the bulb syringe. Are there any mothers or grandmothers who may advise me. I do have my daughter's support as long as it is a last resort.