My family have diarrhea (once), cold sweat and feel a little stinging in hand ,foot and face. is this serious? should she go to er?

Not necessarily: So far you haven't listed symptoms that sound like emergency care is required. We don't know how old your family member is. Is there fever? I recommend continuing to monitor and in the meantime would recommend resting and hydrating with non-caffienated fluids. For many loose stools with dizziness, chest pain, new onset of confusion or high fever - would recommend more emergent assessment.