Hi. Your granddaughter has chosen a good hobby. Great to hear about budding gardeners. When I pick the seeds, I wait until the pod is brownish and dry. It will probably crack open to reveal black seeds. Sometimes they're shrivelled and sometimes nice and plump. I dry them at room temp for a week and then put them in a paper envelope and store them in the frig for 3 weeks and then plant them. Some people soak them with hydrogen peroxide solution but I find it doesn't really make much difference. Most gardeners have found what works best for them. Hopefully someone else will chime in here and give their method.