I'm able to step away to the door where I generally wait a few minutes to see if she's going to cry or remain settled and quietly exit.
This is where she and you are stuck, with you at the door.
I suggest your usual routine but you step *out* of the room, yes she will call back because she is stuck at a place where she feels safe with you in the room, so go back, then *out* of the room again. Do this for a few days only. Then you need to take the next step which is either (I don't know if you shut her door for her to sleep or not)
- out of the room and shut the door (if you do this you still return on call backs then out and shut the door again)
or
- out of the room and down the stairs (straight to this if the door is left open - she needs to know you have gone and she needs to know you still come back)
Admittedly the second one there does mean you get some leg exercise up and down the stairs, the thing is if you continue at the door in the room or move it on to outside the door with the door open she can still get 'stuck' at that step and be waiting to hear you stay/leave which means when you leave she still has 50:50 chance of being disturbed by it.
Alternatively if she is calling back but not screaming or crying you can stay outside the door (with it shut) and say your key phrase from outside the room. It may be helpful to use this in conjunction with stepping to the door, out the door and shutting the door (and even from half way down the stairs if you decide to stop their!). It reinforces the key phrase and reassures her that you are still watching out for her and keeping her safe even though you are not in the room. Obviously if she really needs to yout go back in you do.
WRT BT WD, some LOs at this age become too stimulated by a bath I think Tracy suggested moving bath to another time of day if this was the case. Maybe give it a go? Also books may well be too stimulating at that time, I know many people like to get BT reading secured in the routine but if you read at other times of the day there is no requirement for it to be at BT. I did not do BT reading with mine until he turned 5yo (and he started reading at 2yo, fluent reading at 3yo).
It might also help to look at her day sleep routine to see why BT is taking such a long time to settle.
Your husband may be right that she is OT, LOs moving to 1 nap often do become OT it's quite normal and you can't necessarily avoid all of it. Sometimes when LOs need to move to 1 nap OT can be caused by not being fully on one nap, the lack of consistency of having sometimes 1 and sometimes 2 naps means they cannot get settled on the routine and start to sleep better at night. Some people find they can do 1 nap and 2 nap days and mix it around, some people find they have to go all to 1 nap to enable LO to regulate their sleep and sleep better.
hope this helps