The meaning of 'as easy as not'
Solution 1:
It means there are two options of equal value.
In your quote, Emily pretends she could continue to ride with everybody, or walk, it is all the same to her.
I could pick up your mail for you while you're gone, as easy as not.
This means that while you're away on business, I could pick up your mail for you - or not; it's all the same to me.