"How do you make one full cinematic meal out of that, let alone three?...Ms. Walsh and Ms. Boyens, a former teacher and hard-core Tolkien fan, said part of the solution came from Tolkien’s appendices to “The Lord of the Rings.” Those materials helped the writers create a bigger part for Gollum, a fan favorite..."

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Does this mean we'll see Gollum in TDos and/or TaBA?

2463 [ . .] About this time Deagol the Stoor finds the One Ring, and is murdered by Smeagol.
2470 About this time Smeagol-Gollum hides in the Misty Mountains.
2941 [ . .] Bilbo meets Smeagol-Gollum and finds the Ring.
2942 [ . .] Gollum leaves the Mountains and begins his search for the 'thief' of the Ring.
2951 [ . .] Gollum turns towards Mordor.
2980 [ . .] About this time Gollum reaches the confines of Mordor and becomes acquainted with Shelob.
3001 [ . .] Gandalf seeks for news of Gollum and calls on the help of Aragorn.
3009 Gandalf and Aragorn renew their hunt for Gollum at intervals during the next eight years, searching in the vales of Anduin, Mirkwood, and Rhovanion to the confines of Mordor. At some time during these years Gollum himself ventured into Mordor, and was captured by Sauron.
3017 Gollum is released from Mordor. He is taken by Aragorn in the Dead Marshes, and brought to Thranduil in Mirkwood.
[2018] June [ . .] 20 [ . .] About the same time Thranduil is attacked, and Gollum escapes.
August All trace of Gollum is lost. It is thought that at about this time, being hunted both by the Elves and Sauron's servants, he took refuge in Moria; but when he had at last discovered the way to the West-gate he could not get out.
[2019] January [ . .] 13 [ . .] The Company reaches the West-gate of Moria at nightfall. Gollum begins to trail the Ring-bearer.
February [ . .] 16 Farewell to Lorien. Gollum in hiding on the west bank observes the departure.
29 [ . .] Frodo descends from the Emyn Muil and meets Gollum.
March [ . .] 11 Gollum visits Shelob, but seeing Frodo asleep nearly repents.
12 Gollum leads Frodo into Shelob's lair.
25 [ . .] Gollum seizes the Ring and falls in the Cracks of Doom

Similarly smial (or smile) 'burrow' is a likely form for a descendant of smygel, and represents the relationship of Hobbit tran to R. trahan. Smeagol and Deagol are equivalents made up in the same way for the names Trahald 'burrowing, worming in', and Nahald 'secret' in the Northern tongues.

Everyone agrees, however, that credit for one of the most well-known scenes in the "Rings" trilogy goes to Ms. Walsh. She had a "eureka moment," as Ms. Boyens put it, while working on "The Lord of the Rings: The Two Towers" and suggested at the last minute that Gollum, a character who started out as a type of Hobbit but becomes mad and addicted to the ring and its power, should have a conversation with himself. The idea was to crystallize how different parts of his mind battle each other and the pain it causes him.
"It's a universal moment for people," Ms. Walsh said. "We all have that voice inside: You're not good enough and you never will be and you’re a failure. I certainly do.”

Complicating that task even further, the screenwriters did not have the rights to Tolkien’s posthumously published “Silmarillion,” an early draft of which was written as a follow-up to “The Hobbit.”

I find it quite amazing that she doesn't even allow herself to be seen on set (to outsiders, that is).

Obviously, I understand it's her wish (and right) to be out of the spotlight.