My one-year-old dog suddenly doesn’t like doing tricks and getting treats? Before, I brought out the treat bag and yelled “let’s do tricks!” she’d come rushing over, but now she turns and walks away with her tail going down between her legs! – Sejal Ghosh, Kolkata
Reframe your thinking here, for her benefit. She now has a negative association with training. If her tail is between her legs most likely means she is a little scared. Did something happen during that to give her a bad experience? Even something out of your control like a loud noise? One bad experience can cause some dogs to have a pretty bad negative association with something. It could even be that she heard a loud scary person and you yelling “let’s do tricks” reminds her of a loud scary human.
Change up the routine and see what happens. Get the treats out like an hour ahead of time and leave them out of reach (that way there are none of the typical noises). Then, just start out by giving her a treat randomly and see how she reacts. If she perks up and is interested, start working slowly back into the training and see how she does.
Edit 1: To clarify, make sure you get the treats out of the bag, not just get the bag out. Take a couple treats out and leave them on the counter or something. And, maybe worth a vet visit, especially if you are noticing any other weird behaviour. If it’s literally just this one thing, you don’t need to rush to the vet, but, if after a day or two of working on it she still isn’t showing signs of improvement, you’d probably go. Oh, and it may be something completely unrelated to treats or training bothering her, but is a part of the routine. You could do each of the actions associated with training in isolation and see is upsetting her.
Now, just to clarify, make sure you’re not pushing her or overly stressing her. If she’ll take them, make sure you have lots of yummy treats and reward her/just give her lots of treats and love during the entire process. If she has a favourite treat, maybe go get that and see how it changes things. Try and isolate different variables so you can determine what exactly it is your pup needs help with.
Edit 2: Where was your pup when you were gone? Could she have had a bad experience then that affected her?
Edit 3: We would take a break from training entirely for a couple of weeks to let her recover from her scary experience. Work on trust building exercises instead. Rather than trying to teach her a new trick, focus on teaching her that she’s safe around your hands. This is super important for her to learn. Move your hands slowly to different places around her face/head while giving her treats. Make sure you’re only working within her limits of comfort. If you can get your hand next to her snout without her showing any signs of stress or uncertainty, then start there. Once she’s comfortable with your hands around her head/face area, you can revisit this. You can give her added comfort by using a treat on the end of a string or stick (if that doesn’t scare her) in order to lure her without you needing to bend, hover, or loom. Reward the tiniest little steps toward your end goal rather than expecting her to follow a lure into a full spin.