There is no sure fire way to tell about a fever in a dog without a thermometer. You can use a ear one but they are not as acurate as the rectal type. I'd recommend purchasing a digital rectal thermometer. Syringing water is a good idea another would be to add something enticing to it to make it taste better. I've also heard of people using chicken noodle soup. It's liquid and because of the salt content it makes them thirsty afterward.
Keeping my fingers crossed that she feels better soon