The effect of the Donner party is they stopped at a better location with grazing for cattle and shops for wagon repairs. They planned on going fort Laramie but decided to stop at fort Bernard instead which is 10 miles east of fort Laramie because they were warned that Indians were fighting ahead the grazing for cattle was poor at for Laramie and they could get wagon repairs at fort Bernard.
The correct preposition to fill in the blank is between: she had to decide between two things. This sentence indicates that there is a decision to be made, and the possibilities aretwo, which requires the preposition between. (She had to decide between two things, which is to have preference for one thing to another.)
