Is it correct to say "She had never been sick since she started staying at home until she started going to school"?

Look at this diagram

As shown in the diagram, my children had been staying home for a year due to Covid-19. Within that year, they had never been sick.

A week ago, they started going back to school. A first few days within that week, they were well not sick but now they are sick.

Can we use this structure?:

Past perfect or past perfect continuous + since a point of time in the past + until another point of time in the past

Is it correct to say "She had never been sick since she started staying at home until she started going to school"?

I have a feeling that "until" should be replaced by "by the time"

"She had never been sick since she started staying at home by the time she started going to school"

• She was never sick all the time she stayed at home due to Covid. I don't know what you mean by 'they are well not sick but they are sick'. Commented Aug 9, 2022 at 16:47
• In your particular sentence, "since" can be misunderstood to mean "because". Commented Aug 9, 2022 at 16:47
• @KateBunting, Sorry I used the wrong tense, I updated "they were well not sick but now they are sick"
– Tom
Commented Aug 9, 2022 at 16:50
• Oh, I see - you mean they were well for the first few days back at school. Commented Aug 9, 2022 at 16:57
• @KateBunting, yes, I mean that
– Tom
Commented Aug 9, 2022 at 16:59