I wish I had heard about BW before!

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I still get advice from this wonderful community and my DS is 6 years old already. I arrived here when he was 4 months old (lucky me I had a BW book when he was 4wks so he was already an independent sleeper before I arrived - even so we still had our tricky phases and the support here is a life saver!!) and I've never left. The amount of experience shared here is amazing. Just wait, you'll be supporting others who want to sleep train their toddler and letting them know that you've been through the experience and lived to tell the tale

Your progress is fabulous - it's enough to give you the confidence to keep going and you must keep this in mind - if the regression hits just keep calm and remind yourself of these achievements. Your LO is doing brilliantly, she may "test" you to see if you really mean this and that's your chance to show her that you will always always be there for her, that you will always return when needed, it will give her additional confidence that you are still the team you were when you co-slept, you just sleep in different places now

So I figure now's the time to start making my move out the door.
Do i just move my chair further away from her each night until I'm out the door or should I put her down and leave?
This really depends on how well she is going down. You can position the chair further away AND walk out the door.
Lets say you have been right by her said, move the chair a couple of feet away.
Lets say she goes down quite calmly and you are already just watching her nod off rather than having a hand on her. You can leave - say "night night sweetie, call if you need me" and walk out (I would stand outside the door). If/when she calls go right back in, "Okay, here I am, it's okay" and either PUPD or sit in your chair and use a key phrase "go to sleep" or put a hand on her if needed - basically you do your usual thing to settle her back down and this is based on your own assessment of the situation and her level of need. Always responding to need but not more than is needed.
There is no rule about not being allowed to comfort her (the opposite, you should comfort her, it reinforces her confidence in you and in her situation), if you sometimes need to pick her up to calm her this does not change just because you left the room and have started the next step in a gradual withdrawal. Only, when you have put her down and she's calmer you either move back out the door (repeat your phase "call if you need me") or you go the chair. Going to the chair is if it is too much for her/you to handle walking out the door. You always go as far as you can. Make sense?
Let's say it's a bit harder - she is screaming blue murder every time you walk out the door - that's when I'd stop doing that and go to your chair instead. At the chair you can use a phrase "I'm right here, everything is fine, go to sleep" - and from here you can still move to her side, PUPD, use a hand on her whatever needed to calm - then return to the chair and use your phrase.
Do you see how it is a back and forth - it is not just moving away and staying away because what you teach her is that you always come back (and then go again when she is calm).
Over one night or more nights this will start to get easier.
As soon as she is calmer with you on the chair you move the chair, another couple of feet away, and do the whole thing again.
Again as soon as she is a bit calmer you move again.
Once you are out of the room (out of sight) use your key phrase from that position and return to her when needed but use verbal reassurance when you can. Then as above it becomes WIWO (walk in walk out).
It's okay to adapt these methods so long as you do not get "stuck". At no point do you wait until she is just happily going to sleep with you in the room holding her hand or other prop...you keep moving.
Another thing I always did (and I think Tracy did this too) is always always tell my DS I was leaving the room and that I would come back if he needed me. So, even if he was having a very tricky time and I had to stay until he was asleep I still said it, in fact if he was asleep I said it louder so he could hear me. "I'm going now so you can have a proper sleep, call if you need me".
This reinforces (even when asleep) that you will return when needed. It also takes away that sudden shock of waking or opening eyes and expecting you to be in a certain place (on the chair) and then panicking or getting upset to find you are not there.
What you aim for is that she expects you to not be there, you belong downstairs having a cuppa or in bed asleep - but that when needed you will return. She will also learn how long it takes for you to get there, initially you will be just outside the door but when you go downstairs it will take a minute to get to her. What she learns is that you ARE coming, she will be confident in that.
It can feel a bit risky to tell LO that you are leaving the room, especially when you spend ages getting them settled and you know the risk is they start crying again but I found this to work very well for us rather than sneaking away (I think Tracy covers sneaking away in the BW book, it is unsettling for LO to discover you gone).
BUT - it is your choice. You need to do what works for you.
do I gradually move out of the room or should it be cold turkey?
I think the answer is neither - I hope my description helps you find your groove

You can do this!