She does look a little underweight, first of all i would recommend taking her to the vet for a checkup, there might be a medical reason for her being undeweight and this must be ruled out first thing. if she is cleared by the vet, you should switch her food to a high quality grain free diet such as Orijen, Evolve or Taste of the wild, you can feed her 3 times a day until she starts gaining weight.