1. Rent a pontoon boat at the Pokonobe Lodge/Marina on Lake Mary. They rent fishing rods, but sell bait in their store. (OGT lives in Tahoe now.)http://pokonobemarina.com/marina/
2. See above. They also rent kayaks. Or you can drive to the June Lake beach and rent from Mammoth Kayaks...they have SUP's, too. That's where I've been taking my inflatable kayak this summer and you can't beat the views and the warm water. http://www.mammothkayaks.com/#get-started
3. Out of Coldwater Campground behind Lake Mary, drive to the top to the trailhead and hike along the Coldwater Creek trail to Emerald Lake. A nice, short hike and the wildflowers along the creek are going off right now. Picnic up near the lake or when you come back down at one of the picnic tables near the parking lot. Restrooms are there, too. If your daughter isn't tired out after that hike, walk or drive to the upper parking lot and take a walking tour of the Consolidated Mine. (see link for this tour at the bottom of this link ->) http://www.mammothtrails.org/destinatio ... ter-creek/
4. Mammoth Pack Outfit, right up Lake Mary Road heading to the Lakes Basin. Neat rides to Red Mountain with outstanding views. Make a reservation. http://mammothpack.wix.com/mammothpack
If you go to DPP and Rainbow Falls, it's a slog of a hike for a kid (6 miles r/t if you start from the DPP lot - you can get closer to the falls further up; the bus stops in both places) with some steep rock steps in places, dusty trail and not much shade. Wear hiking boots/close-toed shoes, NOT flipflops or open sandals or you'll all be miserable. Bring plenty of water, wear sunscreen and bug juice and wear hats. I couldn't believe how many people I passed last Thursday on my hike down there not prepared for this hike! https://www.nps.gov/depo/index.htm
Take a scenic ride to the top of Mammoth Mountain and hike out to the Lakes Basin overlook. Or hike all the way down the backside hiking trail back to Main Lodge (all downhill, takes about 2 hrs.) If you ride the gondi back down, be sure to get off at McCoy and exit to the right, go outside to their new Mammoth Outdoor Museum and check out all the interpretive panels and their exhibits of old gondi's, old chairs, an old QMC tram car from June Mtn., old snow grooming equipment, a snow Cat you can climb in to along with a little red Weasel you can get inside. Then walk up the marked trail to the east and view one of the snow survey stations. Continue up that trail to see more panels and some of the nicest views on the mountain. Watch for the cliffs though as you're right above Roger's Ridge!
And if those ideas aren't enough you can always go to the Mammoth Lakes Tourism website and search for more ideas. http://www.visitmammoth.com
Have a blast!