Here is what I would do...
Clip her leash on while feeding a cookie, then use treats or her food bowl with her meal to encourage her to walk towards you while having the leash on. Practice this a few times, don't put any extra tension on the leash, just encouragement, stepping a few steps back as she comes, then pet and reward. If she tries to back up or melts down, just ignore her, take a deep breath and wait, try to not acknowledge her. Don't pull forward but don't give into it either. If you have given in backwards at all, then this is now more a learned behaviour than a stress response. Only feed meals after a bit of leash success. When she is happily coming towards you on the leash for a couple quick sessions, step backwards while placing a bit of pressure on the leash and luring/encouraging her forward. She might buck again but just wait. It is important for them to learn to give to pressure in a non stressful way. I'm talking about light light tension at first, and loosening immediately when she gives in the direction. Lots of treats and praise and encouragement when she is doing what you want. When you have this good and fluent, her following you (you taking little steps back) you can rotate yourself to face the same direction as her and continue the effort. Work little bits of leash pressure at a time with lots of verbal encouragement and rewards for success. There are points in a dogs' life that they will have to deal with a bit of pressure, where it is not their choice, and it is important to me to let them experience this where they are otherwise comfortable (ie, not pulled into a room for the first time at the vet's office). Teach the leash as a communication tool, not a management tool. It's your job to keep it loose if she is walking nice, and tension means she is wrong. Teach her to give into tension not oppose it.
Personally - this is my opinion of course - I wouldn't bother with the sniff it get a treat stuff for this very long if at all. If you aren't able to make a game out of it in a couple sessions, just move on. If there is already stress associated you will probably just create more between the two of you if she's not valuing interaction with it. I have seen many people with normal to shy puppies who start off trying to shape a response whenever the pup shows resistance to something end up with don't-wanna-don't-hafta and some pretty negative fallout. Work on your shaping skills outside of desensitization before attempting to change an emotional response. Management over modification. Sometimes exercises like this create extra problems because you are drawing lots of attention to the scary thing instead of just treating it like a normal expectation and no big deal. After raising and training nervous dogs, I have one goal. I want them to learn that trusting me when they are unsure is the best decision ever, from the beginning.
