Cry it out method with 21 month old

[Rhi14]

Hi everyone, I'm sure I will be critisised for this but tonight we have tried the cry it out method for the firs time.
My daughter sleeps well for the first half of the night, but over the last month or so she has started waking up between 1 and 2 and not going back to sleep until sometimes 4-5 am. This is with us going in her room and lying with her, trying everything to help her back to sleep. We co slept until 18 months and now she's in her own bed in her own room however sometimes I end up in with her ( which I'm fine with ) it's just the waking up for hours on end which is the problem .
My partner has said he will not do this anymore and has persuaded me to do something I've never thought I would do. The cry it out method.
This is out first night, she woke up at 2.30am and has been on off crying every since, it is now 6.00am . This doesn't feel right and I am desperate to go in there and comfort her, but know that the night is wasted if I do. The fact she hasn't gone to sleep her , does that mean that it's not going to work with her and we need to try something else.... Or should we persevere tomorrow night.
Also if she's not gone to sleep by the time it's 7 ish, do I just go in there and comfort her and then take her down for breakfast even though she hadn't slept for hours.
Ahhh help

Thank you for eveyrone's replies and I understand people were worried before. She was totally fine and we did check on her, I was just listening to other people rather than my gut!
I am now in charge of bedtimes again and we are in the process of trying the fading out method.
It seems to be working as our daughter is allowing me to say good night and sit right next to the door and she falls asleep within 5 minutes. This is the same for naptime so in the next few days I will try and leave after saying good night. ( Before we would have to lie with her for sometimes up to half an hour )

However
We have a new problem . She is now waking up through the night and soemtimes not going back to sleep for hours. I'm having to sit in her room as I can't get into bed with her after we've come this far. I can't help but think it's because she's anxious about the big changes to her sleep and now her sleep is worse than before !
We've made steps in her being able to fall asleep on her own.. how ever these night wakings are taking their toll. Some nights she's woken up at 12am and not gone back to sleep until 3.30am.
Other night she's gone back to sleep quickly but woken up at 12, 2 and then 4 !
She's also.more clingy with me in the day.
I'm really struggling to.know what to do...
Is this something I should continue with and it will get better ???
Or should I write it off as a bad job

Thanks
Rhian