Awesome!! never seen the ocean huh? She is going to LOVE it!!
The closet beach would probably be Cocoa Beach, which is a great beach, but as you have expressed a desire to forego the more "commercial" and heavily populated water fronts, I would skip that one.
(it is a nice beach though)
The beach I would suggest instead is called New Smyrna Beach (you say it like, SEH-MER-NAH)
This beach is more residential and lesser frequented than Cocoa. The other fantastic thing about this beach is it resides within an Art District community. Should you find yourselves melting away on the beach, and want to head in for ice cream and a stroll there are many terrific art galleries, artisan shops, and restaurants or cafes.
Here is a link to their visitors' site and you can take a look before you choose
You will be looking at just over an hour for your commute to this area.
Cocoa and Smyrna are both Atlantic side beaches with Atlantic ocean waters. I will tell you this... the beaches on the Atlantic ocean differ from what you will experience on the Gulf side. The Atlantic beaches have rougher water with more waves and windier beaches. They also have rougher sand. Coarser sand aside, you will still find those tropical white sand sprawls at Cocoa or Smyrna, with shell hunting and everything you would expect beach side. When I say, "rougher water", this isn't something dangerous per-say, you can still swim and enjoy the surf. I would say that average wave heights on the Atlantic are around thigh to waist high, where the Gulf side under calm weather conditions you are looking at like knee to lower thigh wave heights. The sand at many Gulf beaches is a fine powdery quartz crystal sand, and more so the further south you go along the west coast of Florida.
The other difference in Atlantic beaches vs Gulf of Mexico beaches is the water temperature. The Gulf gets MUCH warmer (like, think bath, 85+ degree F and up) and stay warmer longer into the cold seasons. The Atlantic side can see 80+ temps in the summer months but in colder seasons will drop as low as 60... I don't believe the gulf beaches water ever gets cooler than 70.
One more important note between Atlantic Beaches vs Gulf Beaches... you know all those fantastic sunset photos that you see? The ones with a huge orange ball sinking into the sea, and spectacular skies of pink, coral, purple, and orange? Yeah, those are Gulf Beach photos. If you want to experience the magnificent sunsets of Florida, you should probably take the longer drive and head west. The sunrises are gorgeous on the Atlantic side (if you wanna get up that early) but I still think, hands down, the sunsets are the not to be missed!
If you think you might be up for more of a trek, and would prefer to see the Gulf side beaches, you can jog (almost, but not really, more like SW) west from Orlando and head to Clearwater Beach. This is a lovely beach, though, fairly popular. For a drive over to Clearwater you should expect something around 1 hour and 45min, depending on traffic.
Finally, and these last 2 are the longest commutes of all... BUT SO WORTH IT, I promise. (money back guarantee.... if I was charging for this. lol)
Heading further south, and south west, there are 2 beaches along the western central coast on the Gulf. One can be found on a small residential (though, more and more vacation rentals are showing up out there, much to the dismay of residents) island by the name of Anna Maria Island. This island is its own township, but is in the city of Bradenton and County of Manatee. Holmes Beach of Anna Maria is fine white sand beaches, playgrounds, volley ball, cafe, free trolleys to explore the entire island. Easy to spend an entire day here. This town and island has received travelers assoc awards and recognition for, "one of the best islands"
Going just slightly further south you can make your way to a barrier island chain on the gulf coast in the county of Sarasota, Siesta Key. The "key" is more of a chain or elongated barrier island, but Siesta beach has been globally recognized and voted "BEST BEACH IN AMERICA" several years running.
As you can imagine, this has made the beach more popular and there is higher traffic, but the beach spaces are vast, with many public access locations. Somehow, even though it can get busy, it doesn't feel like you're losing out on that tropical escape feel. Just a bit slightly more south of Siesta Key beach is another along the key called, Crescent Beach. Crescent is considerably more "private" beach experience.
("crowded" is a relative term. Because I live in a tourist state, and actually in a fairly touristy town in a tourist state, my idea of crowded compared to your idea of crowded might be very different)
Anna Maria island will take you about 2 hours to get to.
Siesta Key Beach will take you about 2 hours and 30 mins.
Hope this has been helpful to you!! Have a great time, and DO NOT FORGET YOUR SUNSCREEN... ALWAYS reapply as recommended!! (that's probably the best advice I have given you this whole LONG reply)
ALL DRIVE TIMES ARE ESTIMATIONS USED WITH THE HELP OF GOOGLE MAPS. reliability may vary. blame google not me for any errors.