The last step of this quest reads “Hold a ceremony at the Church”, and that is the entire instruction. 
Agatha agrees to come, you hold the ceremony, and she is not there.
The word missing from that line is zombies. A ceremony only counts toward this quest if the choir was singing through it, and an empty choir stall does not sing.
The ceremony only counts if the choir is singing
Building the choir is not the same as having one. The quest checks that the last sermon had choir activity, and the stalls are only active while there is a zombie standing in them.
The difference is visible in the church before you start. An empty stall is worth one on its own and carries a Put Zombie prompt; put a singer in it and the stall reads two and the room goes up a point of church quality with it.
Put at least one a zombie in the choir stall, then hold the sermon. She turns up.
Take the singer out again afterwards and the next sermon stops counting for anything that asks for a choir, so leave it there if you want the church quality as well.
It is worth knowing this is the same pool as your zombie workers, so a singer is a worker you are not using elsewhere. The stall holds up to five, and the Dead singer perk makes one worth more 
Faith than the others.
Building the choir is the step before that
The choir is a Church build and it sits behind its own technology. 
Church Music I costs 
50 and 
20 and hangs off 
Church Carpets, so the church upgrades have to be underway before the node is even on the branch.
| Church Music I | Theology branch, behind Church Carpets | 50 red, 20 blue |
| Music Notes, four of them | Writing Desk | 2 Clean Paper and 1 Ink each, at Book writing 5 |
| The Choir | Church build desk | 4 Oiled Plank, 2 Bronze Detail, 4 Music Notes |
| Singers | The choir stall itself | Up to five zombies, one is enough |
Music Notes are the part that catches people out, because they are a 
Writing Desk job rather than a Church one and they want Book writing mastery of five. Four of them is eight 
Clean Paper and four 
Ink on top of the 
Oiled Plank and 
Bronze Detail the build itself asks for.
Between asking her and assembling the choir there is a quest with no journal text at all. It completes the moment the choir is built, so the line that says “Assemble a Choir at the Church” only appears after you have worked out that a choir was wanted.
If your journal looks like it has skipped a step, that is what happened. The instruction is in a line of dialogue you have already clicked past.
Asking is not the task, because she says no
The quest is called The Nun Also Reads and its objective is to ask her whether she will read for 
Herbert. She refuses, and the refusal is where the actual job is hidden.
Oh, I’m flattered! But no. I have far more important things to do!
Is there anything, even the remotest possibility of changing your mind?
No. Absolutely not… Although… if, somehow, you managed to get a proper choir singing at your church…
But it’s impossible! You can’t find any decent singers these days… They’re all dead!
Agatha, refusing
That last line is the hint and the joke at once. Every decent singer in the region is dead, and raising the dead is the one thing you are good at, which is why the answer is a stall full of corpses.
There is one more step after the choir. She has taken a vow that keeps her at the crossroads, and the way past it is to pick “Be a little creative” and grant her the dispensation yourself.
You know I’ve taken a vow… I can’t leave this crossroads.
Hmm… as a priest, and the highest church official in… the area… I hereby grant you permission.
What… wait… actually… that should work.
Agatha, and the loophole
And she will not discuss it under 20 reputation
Before any of the above, the “Read for my friend” line is locked until you have 20 reputation with Agatha. The objective does not mention it, and the reputation comes from her own thread rather than from the 
Herbert and? chain that handed you the quest.
| Hold the sermon at your Church yourself | The first one, and the one that starts the other two |
| Nun of Your Business | 5 Clean Paper and 2 Ink brought to her |
| Fix the Manhole at the Crossroads | Then report to her |
Ten quests pay her reputation and every one pays exactly ten, so two of them clears this gate. 
Nun of Your Business is usually the quickest, because the paper and ink are the same Writing Desk chain the Music Notes need later anyway.
The whole thread in order
Read top to bottom this is four separate jobs wearing one quest name, which is the other reason it reads as broken.
| Herbert and? | Bring him the Love Novel from the Dockside Club |
| The Nun Also Reads | Ask Agatha, with 20 reputation. She says no and names the choir |
| The step with no journal text | Building the choir at the Church |
| Assemble a Choir at the Church | Tell her it is ready, then give her the dispensation |
| Hold a ceremony at the Church | A sermon with at least one zombie singing in the stall |
The ceremony pays 10 reputation and 2 Town Gratitude, she confesses to not burying her sisters properly and to eating too much candy, and she agrees to read to Herbert on the condition that he comes to her.
Questions about The Nun Also Reads
Agatha said she would come to the ceremony and she never turns up. Why?
The choir has to be singing during the sermon, and an empty choir stall does not sing. Put at least one zombie in the stall and hold the ceremony again and she appears. Nothing in the quest says this.
How many zombies does the choir need?
One is enough for the quest. The stall holds up to five, and each one adds to church quality, so filling it is worth doing for its own sake.
How do you build the choir?
Research Church Music I on the Theology branch for 50 red and 20 blue spheres, behind Church Carpets. Then build it at the Church desk for 4 Oiled Plank, 2 Bronze Detail and 4 Music Notes.
Where do Music Notes come from?
The Writing Desk, at Book writing mastery 5, for 2 Clean Paper and 1 Ink each. The choir wants four, so that is eight paper and four ink.
The option to ask her is not there at all. What now?
It is locked until you have 20 reputation with Agatha, which the objective does not say. Hold a sermon at your Church yourself for the first ten, then either bring her writing supplies or fix the Manhole at the Crossroads for the second.
Why does my journal look like it skipped a step?
Because one of them has no text. The quest between asking her and assembling the choir carries a blank objective and completes when the choir is built, so the visible instruction arrives after the work.
Comes After
More Quests
A Cure for Wellness
A Good Example is the Best Sermon
Any Portal in a Storm
Battles in the Sewers
Book BrokerBrawns and Brains
