I thought that ' cho ' could also mean ' as ' I was marked wrong for writing 'Isabel isn't as big.' In the Tips 'as' is given as one of several meaning for ' cho'
It is commonly used as "as" when paired with "ri". There will be situations when a meaning of "as" is possible but it is more common as an intensifier in sentences like this. Hope that helps.
Cho mòr ri - as big as