Random thought here, but didn't I read someone with a sniffly kitty put her in a bathroom and ran the shower on hot to steam up the bathroom and it helped? I'm an advocate of natural remedies so perhaps eucalyptus(sp) might help as well...steamed in the shower I mean.
Good luck and remind your mom that cats have nine lives and Pyka may surprise her yet Siamese are so fragile and tiny too that her symptoms may be more pronounced due to her size.