Was it a risk blocking Talia's escape route from Squidge?
I was pretty confident that Talia wouldn't aggress towards Squidge. She's an exceedingly gentle dog. So the risk was in over-facing her, and that's why I kept Squidge on lead to start off with, to see what Talia would do. I waited until she started to approach us before I let Squidge off the lead.
There are some things that I would do differently given a younger dog, and one that hasn't spent such a long time in a shelter environment. The fact is that she has over a decade's worth of reinforcement history of escaping to her den when things get a bit uncomfortable, and there is simply no way that I can undo that in the space of a few days, weeks, months... and probably not even if I had years. So if I want her to progress, I have to push her harder than I would in a different situation. My choice was to spend potentially weeks and months trying to associate Squidge with good things (which is very difficult when she is hiding away and can't even see us), or risk slightly over-facing her and relying on Squidge's charm to win her round.
I made the same decision with regards to the collar. She is so afraid of slip leads that I don't see myself being able to counter-condition effectively in any reasonable timeframe: again, there is a huge amount of learning history around them being used to trap her for vet checks etc. So I decided that, instead of wasting time on that, I would pop a collar on her so that I can more easily attach a lead later on. Yes, it meant that I had to make her uncomfortable while I clipped it on in her den for about thirty seconds, but it was done and over, and that was that.
Is it the perfect scenario? No. But it should lead to her being able to fit into the family sooner, and so to me that justifies the moments of discomfort for her.