My 7 1/2 yo just finished TRL at the end of last year. My 10yo used this as well, back in her younger days!
Even though your child knows the phonics in the first lessons, and more, I think you will find this book will still be very beneficial to you. There is a lot in there, and the beginning lessons are much lighter than what it ends with from a child's reading ability standpoint. You may find that at first she soars through the lessons either doing them quickly or doing more in a sitting. It may stay that way, or after a bit she may slow down to a normal pace.

At the end, you can expect your child to go into the Emerging Readers with no issues. My dd is now reading The Beginners Bible that comes with BLHFHG with no issues, and moving at a fast pace.
We also used the Rod & Staff spelling for quite a few years. If you like it, there is no harm staying with that if that is what you desire to do. The spelling is easy to teach in HOD. If you are looking at using Bigger for your son, I believe that guide has a few levels of spelling lists to choose from, or going right into dictation. The spelling does not include any phonics info like the R & S spelling does. In the dictaction, they must copy it correctly including all proper punctuation. Grammar comes through the English lessons.
We stopped the R & S spelling, even though we liked it. It was a bit too much for my girls to have grammar in with their spelling on top of it already in their English. Reinforcement is good, no doubt, but too much of a good thing on some days wore this mommy down (girls moaning over doing too much, etc). After a bit I realized, too, that I felt better fully utilizing the HOD guides as they were and using the spelling provided in the guide vs. paying more for something else on top of it.
17 yo dd - finishing WH, Geometry, German, Music, Media Art - filmaking, stop animation, etc.
14 yo dd - finishing RTR & TT7, Piano, Animal Shelter Volunteer.
11 yo dd - CTC, finishing up TT5, Piano.