If you are trying to maximize the minutes for 4 players to cover 3 positions, so you don't have to use a 5th much, you only have one sub available for 3 positions. After the first substitution it is still one sub for 3 positions, but the available substitute is the first taken out who is catching her breath.
Substituting more than one at a time is impossible without increasing the minutes of the 5th or 6th option. It is very restricting and can even minimize the ability of a coach to do strategic substitutions, because the bigger issue is managing the minutes. Now if Ines does well enough that you don't mind her taking minutes from Azzi, Caroline, Nika or Lou that is not an issue. Or the same thing with Aubrey or Ayanna playing the 3 well enough that it's ok for their time there to eat into the main four's minutes.
If you want to minimize minutes from the 5th or 6th small options, and get as many as possible from your best 4 your hands are pretty much tied. We have very good talent in our top 4 for positions 1-3, but limited flexibility unless Ines, Aubrey, or Ayanna are good enough to take minutes from the top 4. If that happens the flexibility managing minutes returns. I hope it does, but while potential seems to be there, I think the jury is still out on who the 5th and 6th options will be and how good they will be. I think Aubrey has already proved herself to be a very good 4, and I fully expect Ayanna at the 4 to be excellent as well. For the sake of this discussion the question is how good either will be at the 3.