Harness and lead gnawing

UK. 6 month old puppy. 4 days post Rescue. We saw this with her at the rescue and it doesn't seem they had time to try fix it.

If she notices her collar she'll try to chew it. If you put the harness anywhere she can see she wants to chew it. Trying to put it on her is an absolute nightmare of throwing food on the floor so she doesn't notice you trying to get the harness on.

It's a larger one of the rescue, we had to cut the smaller one off of her as she got stuck with her arm in the neck hole and we couldn't manoeuvre it without being bit. It has to go over the head.

If you take out the lead she also chews that. If you give her slack or let her take the lead she'll sit down and chew the metal bits on it. If you don't take her out for a walk fast enough she'll start chewing it, which when trying to teach her not to pull is a battle.

I saw this behaviour when we were at the rescue. They'd literally talk about having to fight her into the harness and throwing food on the floor so you have a few seconds to get it on.

I'm trying to teach her to "leave it" for the harness but it only works until her dives for it. And even then she's not got an amazing attention span at this age and doesn't want to sit for more than a millisecond.

Also to note, according to the vet report she has all her adult teeth.

I'm just not sure what to do because it feels like I can't take her for a walk when I know that's exactly what she needs to get her brain tired enough to sleep.