I don't think that this story as written would 100% work as an anime with Inessa as the primary POV character. It was designed to have characters complement C's story, not Inessa's. So the question is really "What's the smallest change you'd have to make to make this work in a visual medium"?
Hm. I don't think we get the story as written as the anime though; this is basically akin to a companion novel that tells the story rfrom a different perspective, so some of the details are likely different because we're seeing things from somebody else's POV, and there is more emphasis on how the events compliment C's character, while in the actual anime C is much more tertiary, given how outside what is clearly her mini-arc, she rarely features in the main plots of the episodes at all. As a result, there's huge chunks of the story that simply... wouldn't appear in the narrative because you're following Inessa or the Saints in general (I suspect that, for instance, the Ida-centric chapters had Ida's POV, because otherwise there is very little content for the episodes at all.)
I decided to actually go through the chapters and see what I think would be likely to be in the anime proper:
EPISODE 12:
- C gets kidnapped and rescued
- C meets up with the main cast
TIME: Probably around 5-6 minutes of screentime
EPISODE 13:
- Inessa finds an excuse to split up to fight Winter Rose
- They meet up with C affter the fight
- Inessa conversation with C after meeting Mr. Noir
TIME: Probably around 6-7 minutes of screentime
EPISODE 14:
- Temp and Inessa meet up after the game and confronting the monster
- Hears part of C's rant, probably near the tailend, though potentially a bit more.
- Potentially the end, where Lupin turns in Avaritia and kidnaps C
TIME: Roughly 5-6 miuntes of screentime
EPISODE 15:
Given that this is something that is buildup for C's mini-arc later, part of this episodei mo probably does take place from C's perspective
- At least part of the conversation with Avaritia,
- Probably part of the conversation with Superbia
- Part of the conversation while C is jailed, explaining Avaritia's flip-flopping mood toward her, possibly her recruitment speech
- C's incident with the tree
- Inessa's meet up with C after the fact (Likely back to Inessa's perspective)
TIME: Roughly 15-16 minutes, if you count the stuff from Inessa's POV. If not, probably around 10-12 minutes
EPISODE 16:
- The conversation with Inessa's parents at the beginning (this sets up for when C is invited to stay full-time later)
- C and Inessa meet up with Lupin, beginning to show Lupin wanting to be friends with C
- Potentially part of the dream as foreshadowing, per haps not, since from Inessa's POV you could see it fully happen anyway
TIME: Roughly 5 minutes I'd say, if you count a bit of the dream, 6-7
EPISODE 17:
- C meets up with Inessa at the beginning, convo about Michael, a bit of the exposition is probably not in there, since the audience would know that already
- Group investigates Mr. Noir's old headquarters
- The tailend of the meetup and bit with Michael where C isn't qualified is definitely shown, a lot of the rest is exposition the audience already knows, so it probbably wouldn't be
- Potentially the scene with C and Ida afterwards
TIME: Roughly 8 minutes
I could keep going but overall if you cut the C POV stuff I actually tihnk it being a decent capturing of the events of the show from Inessa and CO's perspective is decently workable timeframe wise? You would probably need to rush one or two of them where the plotline is clearly substnatially different from C's perspective, but that could just mean I'm overselling the amount of screentime those sscenes have, or including scenes that wouldn't be in the original. The main exception, I think, is C's episode introducing Invidia where you would have to basically have it entirely/largely from C's perspective for a lot of it to make any sense whatsoever. Not to mention that we don't know what the first 12 episodes were like, which may have material that lead to even more of this being cut if the foreshadowing becomes redundant in some sense.