Lake Tahoe is a large, fresh-water lake that sits on the state line between California and Nevada. It's known, of course, for its casinos and resort areas. In the summer, the water skiing is excellent. In the winter, you can snow ski and snow board. There's a lot to recommend at Lake Tahoe. If you want to get away from it all, the Lake Tahoe Nevada State Park is a large system of parks with lots of recreation options for dogs and their people.
If it's hiking you like, Lake Tahoe has several trails of varying difficulty. Some trails are more improved than others, and some trails can be very steep. There are no off-leash trails on the Nevada side (there are off-leash trails on the California side of the lake). The park is open year-round, but please remember that you will be at a high elevation, and the area is known for its snow. Actually, you will not be far from where the Donner Party spent the winter. So make sure you are adequately prepared for the weather conditions.
There are a number of lovely freshwater lake beaches. Arguably the best, Sand Harbor, outside of Incline Village has a nice, broad beach, with plenty of parking, easy access, and lots of activities such as swimming, snorkeling, and boating. Your dog is welcome from mid-October until mid-April, due to the popularity of the park.
For a less populated experience, try Spooner Lake. It has campgrounds, both primitive and drive-up, as well as cabins. You can easily reach the backcountry with trails for more experienced hikers, and in the winter, there is cross-country and alpine skiing. As with the rest of the Lake Tahoe Nevada State Park system, your dog is welcome as long as she is leashed. Bear in mind that Lake Spooner is more remote than other parts of the park, and plan accordingly.