Pretty sure TL = Typhoon Lagoon.
I've picked an oyster from the store in Japan Epcot and had it set every trip beginning in 2009. I treasure each piece.
As you might expect, gold settings cost much more than silver.
In 2009, I had my 7mm golden pearl drilled with a 14K bail. In 2010, I got a swirl cage pendant that has since tarnished badly. It is a beautiful 7.25mm white pearl, and I'm thinking about bringing it this fall to have a white gold pendant bail drilled into it.
I picked twins in 2011, 6mm golden pearls that I had made into 14K studs to match the 2009 pendant. In 2012, I got my favorite piece--a white 7.25mm pearl set in a silver open clam shell.
I've paid for some really useless souvenirs at WDW over the years, but IMO the pearl jewelry pieces I acquired at Pick-A-Pearl have been great buys since I can wear them for many years.
One piece of advice if you're looking to keep costs down--bring your own chain. You can usually do better elsewhere on silver and gold chains plus you'll have more sizing options, especially if you shop on-line.
Hope your DD picks a great one, OP, and enjoys doing it as much as I have over the years.