It will take her body awhile to adjust to a solid diet. Breastmilk is so easy to digest that it's not unusual for breastfed babies to become constipated when they start solids (well, I think so anyway). Do you offer her any water with her solids?

If you suspect she's constipated again, some diluted prune juice or brown sugar in water can help. Oh, and pears are great too...I usually keep some jars of pureed pear in the cupboard, just in case.