From Wikipedia

Skookum is a Chinook jargon word that has come into general use in British Columbia and Yukon Territory in Canada, and in the U.S. Pacific Northwest.

The word skookum has three meanings:

1. a word in regional English that has a variety of positive connotations;
2. a monster;
3. a souvenir doll once common in the Mountain States

http://en.wikipedia.org/wiki/Skookum

So I'm thinking she means a high quality oven.

Small chance she could mean an oven that is so old it can be considered a monster. Maybe one of those really old wood fire ones that has a special door for bread proofing