I need to replace several sections of "stockade" type wood privacy
fence. They are rotted and falling apart. I've tried temp fixes, but
they're so bad there's nothing for screw or nails to grab onto.

The posts seem okay, I can't rock them at all, and they are solid at
ground level (tried stabbing them with a screwdriver). So it seems to
be just the picket sections that are bad.

Is this something a lone female can accomplish? I can handle tools,
repairs, etc, but my main problem with projects is having the muscle.
Or would this be a two person job?

Also, would it be better to use screws to attach the new sections, or
is that overkill, and nails are enough?

I would like to say thanks for all the good folks that take time to
answer here. This group has helped me in many ways since becoming a
single homeowner four years ago. When I was married, my ex and I
worked on many projects together. However of course I've come across
projects on my older house that were never an issue when married. This
group is a great source of info.