Mixed up various duration of heeling time.
Mixed up reward schedule. Got in a short heeling rep where I did not food reward at end of command and another short rep where I rewarded only at the end. Also tried to space out interval  primary reward a bit more during heeling while using more praise to reassure and keep her motivated as we make our heeling duration longer.
Extended our heeling time to about 1 minute 40 seconds in one of the reps.
Also started to begin the Heel command in a few different position (from a sit on my side, or just from standing at my side) as oppose to always starting with the "leg seeking" pattern in order to prevent Nova from thinking that is the ONLY way to begin a heel.
Rep 1:

Rep 2: