I would say you will be fine dropping R&S grammar. The grammar in Primer is very gentle and natural (drawn from the model), but we really do not begin formal, sequential grammar instruction until students begin Aesop, somewhere between 3rd & 4th grade in general. For Aesop, we have included grammar instruction in the course, and no additional grammar is needed. When students start Homer, we recommend a formal grammar program alongside, and our favorite is Harvey's, but you could certainly substitute R&S 5 or 6 at that point.
As far as dropping the Phonics is concerned, that would probably also be fine if you are getting adequate review in Spelling. The phonograms and spelling covered in Primer are also natural and contextual, so it will not necessarily cover every concept from a systematic phonics program, and certainly not in the order it would covered systematically.
You may be able to cut back on the Cursive practice you are doing if you have your student do her work in cursive for Primer, as well as some of the readers you are using.
We do recommend memorizing the poems and Scripture included in Primer. If you are starting in November, you could begin with Winter, or Fall, whichever you prefer.
Let me know if you have any further questions!