Flooding is not covered by renters insurance (or homeowners insurance, for that matter). If you live in an area at risk of flooding, you should buy a separate flood insurance policy. Don't rely on your landlord's insurance--whatever flood protection she has won't cover your belongings in the event of a flood.
You can check whether you need flood insurance at the National Flood Insurance Program's FloodSmart website.
Keep in mind, though, that your renters insurance policy probably covers water damage due to burst pipes, overflowing bathtubs, and similar situations where water damage is not caused by a natural flood.