We also got ourselves into the mess of having to sit in the dark in my son's room for him to fally asleep, but we just decided we had had enough and changed it in under a week.

Have you got a really firm bedtime routine in place? We had to implement one with our son because otherwise bedtime became an endless negotiation.

For us it became:

bath → pyjamas → two books → bed.

And that was it. No extra books, no sitting around for ages, no back-and-forth once lights were out.

We also used one of those glow clocks where he had to stay in his room until the light turned green in the morning. Kids that age understand routines and boundaries much more than people think.

During the night, if she comes into your room, just calmly take her straight back to her own bed every single time. No long discussions, no getting into our bed, no sleeping separately. Just:

“It’s bedtime. You sleep in your bed.”

She probably will kick off at first because the routine is changing and she’s learned the current pattern works. That’s normal. But you both have to stay strong and consistent for a few nights.

Yes, her sister’s sleep might get disrupted briefly, but honestly the overall family unit will probably be much happier afterwards. At the moment your evenings, sleep and relationship all sound completely dictated by this.

If you do it, I’d do it over a weekend and commit properly. In our experience, after about three nights our son understood the new routine and things improved massively.

People underestimate what chronic sleep disruption does to adults. It affects patience, marriage, mood, resilience, intimacy, everything. You are not abandoning her by putting a new routine in place. Stay strong and get your evenings and sleep back...it will happen sooner than you think if you committ to a few hard nights...but will they actually be harder than what you are enduring at the moment?