My 18 Month Old Granddaughter Has Been Crying A Lot,

My 18 month old granddaughter has been crying a lot, was not eating much . she had no fever, normal stools but possibly dehydrated. I am a neuro nurse and I noticed her arching her spine back. She has just started eating now and drinking. Her main symptom is real clinginess to dad and mom, mostly mom. I know separation anxiety is normal for this age. Should we worry about her arching her spine and what could that mean?