Your categorizations are weird to me, Sure Dwarfs and Gnomes sometimes have overlap in some books (With both being potrayed as Short, Ingenious, Hairy), Though I think this is the minority, most I think treat them as a goblins much smarter cousin, tying in a keen comprehension of mechanical things and magical constructs, I'm not sure why you are comparing them with Halflings (Halflings are just short humans, Tolkien created them to represent the reader, normal humans in a world filled with "larger than life" characters).
Personally I tend to think of gnomes as the missing link between Goblins & Dwarfs
What does her culture have to with your comment about height
Are you seriously calling my beloved Sequoia "Enemy Fodder", or are you talking about Shakala? The MC's children? Obea?
Dude you need to check your racism
Hell yeah! she does, and with a smile too

still not sure what your point is though
I'm not convinced, she's the MC's
Half sister after all, whats the other half? Fairy, Pixie, Carebear? and don't tell me she doesn't have any snuggle bunny in her DNA
The bottom line is there are lots of (short) characters in this game, I don't see how a Gnome would tread on any toes.
- Gnome vs Dwarf, smaller, quicker, more intellectual, more magically inclined (and a lot skinnier)
- Gnome vs Halfling, I don't see any real comparison except both being short
- Gnome vs Goblin, much smarter, much less aggressive.
- Gnome vs Swamp elf, I don't see any real comparison except both being short
- Gnome vs Imp, I don't see any real comparison except both being short
TL;DR I don't see any real overlap in the current population, I imagine a female Gnome would look like a slender Goblin, with human skin tones/hair. With quick, nervous energy... always moving... always curious.