3 year sleep regression

[Becksiv]

DD is 3 next month.
Always been a great sleeper. Sleeps all night, in her own bed and falls asleep by herself.
I've always been one for not creating rods for my own back.

The last week she has started needing us in with her to fall asleep. Without she'll scream and cry for us. She's also started waking in the night frequently, and again needing us to be there to fall asleep. Sometimes it can take 1.5 hours to fall back asleep.
She's two weeks in to sleeping in a toddler bed after taking the cot sides off.

Lots of talk about a regression at 3yo.
How did you handle it?
Lying on her floor whilst she falls asleep is totally not sustainable. We are beginning to lose our sanity

Also have DD who is 13 months so we're trying to limit 3yos crying.

Should we have a few crappy days/nights of not going in when she does this?
I fear so much about causing lasting mental damage.

Our DS did this around 3, suddenly needed us to lie on the floor beside his bed or he wouldn't go to sleep, and coming in beside us in the middle of the night and refusing to go back to his own bed.

I was pregnant at the time and just couldn't do it longterm so we started sitting in a chair in the corner instead of lying beside him, also put a stair gate back on his door so he couldn't come into our room and just dealt with a few weeks of screaming and being firm that his bed was the only option. It was tough, but he is now 3.5 and is back sleeping 11/12 hours a night again and can fall asleep independently.

I also checked he wasn't too hot/cold/bad dreams etc and gave appropriate cuddles if he was upset due to that, but I got very good at telling if he was genuinely scared or upset air if he was just shouting because we stopped him getting his own way.

I bought her a double bed. Now if she needs me, I just get in with her and go to sleep.

We introduced a glo clock for DS when we moved him to a toddler bed and it really made a massive difference. We also have a guard on the side still (a travel guard) just so he still feels a bit contained. Not sure if either of those might work!