Whereas Shani spends the rest of the game trying to erase Geralt from her mind,
No, she doesn't. She spends the rest of the game bravely setting up a field hospital in the middle of Old Vizima -- in the middle of a war zone. Geralt can fight, and Triss can cast spells or teleport out, so neither of them is in much personal danger from the war. Shani is 100% human and doesn't have any combat training, but she packs up her black bag and goes to the war zone, anyway, because that's where people are being injured, so that's where she's needed. I admire the hell out of her for that.
She's a bit snarky the first time she and Geralt meet in Act V -- at her field hospital -- but after that, she starts acting like a friend again.
Triss continues helping him with the Salamandra, the authorities and even Alvin(the amulet).
Yes, but she doesn't do it for him
. It's not that she's helping
him, it's that their objectives happen to coincide. She wants Alvin's power controlled, and she wants Salamandra's power broken.
Geralt could have completed his journey without ever meeting Shani, but he could never have done it without Triss.
Since witchers are immune to disease, of course they have more need of sorceresses than of doctors. On the other hand, sorceresses can cause them a lot more trouble than doctors, too -- just look at Yennifer.
Want to be IN a computer game? I'm making one, and I want a picture of you! See here
I've made three new adventures for TW1; you can get them at corylea.com/
I've also made a bunch of mods that fix bugs, kill annoyances or tweak gameplay; you can get those at the Witcher Nexus