Hello Brian and Alison,
I recently came online and see that your question about Kathy hasn't been answered. I'm so sorry that you've had to wait for a response,but if you still need assistance, I'd like to help if I can.
As you may or may not know, well-cared for terrapins can live 30 years or longer so, hopefully, the following information will be helpful to keep Kathy well for the few months you'll be her caregivers.
I'd like to give credit to Anna who is an expert on this site who compiled this information in it's present format. She has given me permission to use it in answering questions on this site:
Baby sliders only need 15 gallon tank but older ones such as Kathy will need a 60 gallon tank, so hopefully, this is what you have. You can also use a large RubberMaid tote; they aren't as attractive but cost a lot less and get the job done. Set up the tank so there's a land area and a water area. Put the basking light at one end so the whole tank doesn’t get too hot. The water should be about twice as deep as the turtle is long. For example, if the turtle is two inches long, you'll want four inches of water.
Temperatures and Basking Area
Turtles need certain types of lighting and need to be warm; otherwise, fungal and respiratory infections can develop as well as unhealthy shells.
Turtles must have a basking area where they can get out of the water, dry off, and bask in very warm light. The ambient air temperature in the tank should be around
75 *F (24*C) , with the basking area warmer still.
Over the basking area there should be some sort of lamp that will take a 40-60 watt incandescent bulb (or you can buy a ceramic light fixture made just for reptiles). If you live in an area that has farm stores, you can buy a metal light fixture made to keep baby chicks warm for just a few dollars. Don't buy the accompanying bulb, however. You need an ordinary incandescent bulb in the basking light. Hardware stores sell similar fixtures as work lights. The basking area should be kept at 85-90*F (29 to 32*C). Use a digital probe thermometer to be sure. You can adjust the temperature by raising or lowering the light fixture.The lights that come with the covers on aquariums are not suitable for turtles. You'll also need a submersible aquarium heater that will keep the water 78-82*F (26 to 28*C).
It's extremely important that you buy an additional light that produces UVB rays. A Reptisun 10.0 is a good brand. If you choose another brand be absolutely certain it provides UVB rays. Don't take the word of pet store personnel, but read it for yourself. Full-spectrum, DayGlo, sunGlo, UV, or UVA are not the same thing. I'm putting a lot of emphasis on this because it's crucial to your turtle's health. Without this light, Metabolic Bone Disease (MBD) will develop because your turtle won't be able to produce vitamin D. Vitamin supplements are not a good replacement for the proper lighting. MBD causes a very slow and painful death.
UVB bulbs must be replaced every six months as they lose their effectiveness after that, even though they may still look fine. Light that comes through a window isn't sufficient because the glass filters out most of the rays turtles need to stay healthy.
To prevent MBD, turtles also need calcium. The easiest way to provide it is to place a cuttlebone in the tank. Cuttlebones are sold in bird departments of pet stores.
Turtles are very sensitive to water quality. Even if you change the water every day, it can still contain harmful chemicals. A good filtration system is essential. Water changes are also needed even with a filter. If the tank is too small, no filter can keep up with the amount of waste that turtles produce.
Commercial food should make up only 1/4 of the diet. Animal products (cooked meat, earthworms, canned cat food) should make up another 1/4. The remaining half should be plant foods (dark lettuce like romaine, bits of strawberry or melon, etc.). Older turtles should be fed 3 times per week. Overfeeding can lead to gout and kidney failure.
For Further Reading
These two sites are among the most reputable sites on turtles.
I hope this helps; again, my apologies for the delayed reply. Deb