Three weeks is a long time for two women to spend in one small cabin together with almost no intercourse with the outside world.

Little by little, Kate's opinion of Marion had changed considerably.

To go to shows with Marion, to have her at the house for dinner and to spend a night now and then, to lie relaxed upon a cot in the Martha Washington's beauty booth while Marion ministered to her with soothing fingertips and agreeable chatter, was one thing; to live uncomfortably--albeit picturesquely--with Marion in a log cabin in the woods was quite another thing.
Kate began to doubt whether Marion would make a suitable wife for Fred.

She had discovered that Marion was selfish, for one thing; being selfish, she was also mercenary.

Kate began to fear that Marion had designs upon Fred for the sake of his timber claim; which was altogether different, of course, from Kate's designs upon Marion's timber claim! Besides, Marion was inclined to shirk her share of the cooking and dishwashing, and when she made their bed and tidied the crude little room they called their bedroom, she never so much as pretended to hang up Kate's clothes.