What do FAA DERs require regarding low-level requirements in DO-178C?
One thing I would start with is that low level requirements are not the same as derived requirements, although low level requirements can be derived. Derived requirements are requirements that cannot be traced to a higher level requirement.

For verification of DO-178C Level C software, your SVCP will need to completely cover high level and low level requirements as well as attain 100% statement coverage of your code.

As far as what the DER for your project will approve, there really isn't any way for us to know.