This is true, and was not meant as a slight on the general intelligence of someone who cannot read or suffers from dyslexia. I should have made it clear that I was referring to "reading" a riddle, though as has already been pointed out, the Riddler has a penchant for wordplay which might render it hard, if not impossible for her.
Would she be aware of the difference between "to" "too" and "two" for example, if she doesn't know that the Riddler might pun one for another?
jarrodrussel makes a good point about Babs potentially being her "reading eyes", though that would tie up two heroes on a mission where one might do, if they could read for themselves.