Debbie,
LHFHG doesn't use DITHR because it is assuming your kiddos are still doing phonics. Once you get to Beyond and Bigger, DITHR is mentioned as the independent reading option. It is not scheduled, however, as there is just a reminder to do it in the plans. By the time you get to "Preparing..." it is scheduled 3 days a week, but you still have choice about which order to use the units in. This is because DITHR has its own Teacher's Guide and Student Books.
Blessings,
Carrie