Just wanted to chime in and say you have been doing a fantastic job and it has been fun to watch you guys progress. You do a great job with line handling skills and allowing Elle enough time to figure it out on her own without adding pressure.
In the “Elle 2” video at about the 0:37 mark you do a nice job of staying with her and keeping her engaged. This is critical later, an it is a beautiful example of staying engaged. You’re doing a great job.
If you see her do a nose target on truffle odor, which it almost looks like she does there, reward heavily for that. That is a fantastic precision skill that will be helpful later, and if you can build it in now to a behavior chain because she offers it, awesome!
It would be great to practice, as you are with pillows, towels, and blankets, but build to the level where she is actively engaging moving the obstacle out of the way to find the source, even with her nose through prodding. Try using a flat towel on the ground and place the target under an edge a couple of inches in (you may have already done this). This is a tad tough scenario as the towel is trapping some of the odor but once she hits the scent column it would be interesting to see how she engages with the odor. Does she put her nose on top of the towel at the source, or does she push the towel out of the way to get at source? If you can, allow the target to cook in this scenario for at least 5 minutes.
You can begin to change the criteria for reward a bit, and lengthen her active engagement with the target. You already have a pretty nice re-alert going, and she stays really nicely engaged with you at source (which is fantastic on your part) but we want to build to very identifiable alert.
You guys are really doing great together, keep it up.