Is the ghusl considered valid if the person performing it experiences intrusive thoughts about the intention for purity and a lack of care in the ghusl, leading her to feel impure?

Your ghusl is valid as long as you intended to remove the ritual impurity (hadath) or to permit that which is not permissible except with ghusl. You must strive against these whisperings (waswas) and repel them by not giving in to them or paying them any mind, for giving in to whisperings brings about great evil.