Brake Fluid or Coolant Leak?

Since the fluid seems to be under the car, it could be something you pick up while driving. Not necessarily from your own car.

Do you carry brake fluid and coolant with you when you leave the house?

Low brake fluid can indicate the brake pads being low or it can indicate a leak. You should check that out.

 

I doubt brake pad wear at that low of mileage would be enough to cause low fluid levels. The difference between coolant and brake fluid should be fairly easy to detect simply by feel (significantly different viscosities and smell). From the appearance and location I would bet brake fluid.
Either one leaking is worth a trip to the dealer, one for safety reasons (brakes fluid), the other for the damage to the inverter (coolant), seeing it is on the driver’s side. That inverter is expensive!

 

All this tracks with a leak in the brake fluid reservoir (cracked?) or downstream from there. Isn't the brake fluid reservoir near the bulkhead on the driver's side, above the area of the puddle behind the driver's side front wheel? The Braking Power Low warning light is certainly tied to the fluid level in the reservoir--it was ON when you observed low fluid level and went OUT when you refilled. I wouldn't mess around with possible loss of braking. This needs to be checked for leaking starting at the reservoir and downstream from there. If you do suddenly lose braking, don't forget about the parking brake and even B mode to help slow down and avoid a collision.

 

My understanding is that all of the panels come off, but I don’t know exactly what is underneath that one exactly. It is pretty much directly under the brake fluid reservoir assembly.

 

Brake fluid is hard on paint?

 

Pray it's not your brake booster that needs replacing! (Big bucks, no whammies)
There's a panel over the brake fluid container that has clips to allow access but you should be able to shine a line in there and see if you see anything leaking. My wife has the same car and, at last check, her brake pads were still around 6 mm...not even close to needing changing.
Since you're in Colorado, I suggest taking it to a Christian Brother's automotive shop to have them inspect it. I've used them in the past for brake issues and always pleased with their professionalism and honesty and not trying to rip me off or up-sell stuff I don't need and they will use only Toyota OEM parts if you want.