lacking muscle groups

Abs and calves are some of the rare groups where more is almost always better IMO. They are fine to work every day in moderation. I have experienced the best rate of growth in my calves by working them lightly every day in addition to dedicating a full workout to calves once a week where I really punish them. They also responded really well when I stopped loading 500 lbs on the seated calf machine and dropped down to half that weight and concentrated on quality tension over the full range of motion.

Abs can take a beating every day. I have gone as high as 20 minutes a day, 6x per week with difficult ab exercises, and have never found a limit that overtrains them. If you do start training them daily, ramp up slowly so they can adjust. I always do them at the end of my workout though because they are important stabilizers in other movements.

These are personal anecdotes that have worked for me and some others, so YMMV. Some top bodybuilders treat them like every other muscle with low frequency splits and do just fine. It won't hurt to experiment.

Good idea to start a workout with lagging body parts. Whatever part you want to grow, work it out first. Abs will only show when you're low enough body fat but I disagree when people say that abs are only made in the kitchen. They are revealed in the kitchen but in order to have development there, I find it helpful to target them specifically.
I have a hard time getting any pack abs as a female lol even when lean enough.

I'd work them just like any other muscle to be honest. High volume and progressive overload.