A 2 y/o F presents to the ED with a 3-day history of vomiting and diarrhea. Viral gastroenteritis has been going around her daycare. Her vital signs are as follows: T 37.5 HR 105 BP 83/52 RR 20 SpO2 99%. On examination you find that she is fussy, has dry mucous membranes, and is not producing tears. Her peripheral capillary refill is 3 seconds. Her skin turgor appears normal and you do not note particularly sunken eyes. Which of the following is the MOST appropriate initial rehydration strategy?