Thistle's at it again!

Well all has been going swimmingly with Thistle, but know we seem to be going backwards again, I'm aware that she would now be classed as a teenager, and she is in the full throws of teething, but she is also a much bigger dog, so what worked before re: Biting, snarling, jumping and ripping clothes is a bit harder now, she is a lot better regards these behaviours but recently we seem to be going backwards. She has also decided that she doesn't want to go in the car, she goes in the boot, I have been picking her up to put her in, which usually isn't a problem, but she growled and snapped at me the other day, I told her off (verbally) she seemed better the next time, although I guess I was a bit tense expecting her to react but she seemed fine, although not happy about it, but the last time it was a real battle to the point where she bit me, she curled her lips and showed her teeth and got me on the back of the hand, it seems to be one thing after another with her, she's constantly trying to assert her authority over me.
What I did.
Took her on her long lead. walked around the car but didn't put her in it.
Went back to the car, opened the boot and put down the back seat.
I sat in the boot while she was outside on the lead
I tempted her with a treat, to cut a long story short she got in of her own volition eventually, I did this a few times.
The next time we went out she was ok about getting in, but today she tried it on again.

Things to point out....New car, possible explanation
Also I lift her in and out because she still has problems with her shoulder and I don't want her to put to much pressure on it, she is on anti inflammatrys
Her all round behaviour is generally good I'm just wondering if I am being too soft on her, it is just me and her in the house and she does get and want a lot of attention, is she just trying to assert her authority and how do I manage the biting, she is a big dog?

Thanks rant over....breathhhhhhhhhhhhhhh

Yes, it could be the new car. Have you thought about getting a 2nd hand ramp so she can get in & out on her own without jumping?

As far as the biting goes, take her right back to basics - "No!", turn away & ignore. If you can't do that because of the circumstances (ie getting her into the car) then use rewards like treats or toys to get her to obey without getting the ump!

You sound to be dealing with it pretty well, and you do sometimes at that age feel to be going backwards but it seriously does get better if you stick at it. As for the car, is there any reason why she can't sit in the boot?

Hi Janey, do you mean 'not' put her in the boot? I don't really want her on the seats and I have my grandkids in the car some of the time so I don't really want her sitting with them when I'm driving. I've just taken Thistle out for a walk so on the way I put her in the boot of the car, with coaxing, praised her and then took her out again. thing is she blows hot and cold and her reactions always seem so extreme.

My fault read it wrongly, it sounds like in time Thistle will get used to it, just new to her right now Xx

Keep at it, they do test our patience at times! x

She will get there I promise, patience & persistence is the key