If the consistency of the BMs has changed with the medication and feeding change, the desired effect has happened. If that has not changed the situation, the problem is something else (not constipation).
I've had older dogs with this issue and it can be hard to diagnose and can be minor issues (from pain with arthritis in the hips) to serious (GI lymphoma, neurological). If you need to pursue this (if you think her BM change is a problem) I'd suggest asking for a referral to a GI specialist.
Doug, DVM