Great job getting her to eat. Sounds like she's doing well. With just a 10 gallon tank I wouldn't worry about another thermometer. Just make sure it doesn't get too hot on the warm side(anything over 90) and you'll be ok. The smaller the tank is the quicker it warms up and you won't see a huge gradient with just a 10 gallon tank.... which is ok, just don't let it overheat