90s, alien ambassadors, biotech, communication with airborne chemicals, woman author?

[sbwoodside]

Setting is Cupertino Library, late 90s, I've been searching for the novel for years now. All I have are images:

• The earth is in environmental disaster, alien ambassadors have come to help clean up. Perhaps the aliens were formerly at war with Earth through a misunderstanding.
• The aliens are not really humanoid, they live in a biologically engineered environment in their houses and communicate both verbally and telepathically using chemical signals.
• The plot is vague, but there are action sequences. I recall an attack on a fortress in a mountain, perhaps attacked from above.

I read every Sarah Zettel novel thinking it was her, because her style reminds me... that's all I have.