Claire welcome to the thread
you are doing all the right things. My dear sister is going through this at the moment with her basset hound who at 10 weeks old and having been with my sister for 2 weeks has finally settled in and is now up for play!! Gave my sis a real fright the other day as puppy launched herself in from the garden went straight for my sister's foot and bit her drawing blood. It was only play, she then lay down and was growling which my sister thought was aggression but it is really not, tail was wagging the whole time she just wanted to play bless her. I also spoke to my sis about what had happend in the day was it any different and sis said yes she had given her outside access all afternoon instead of managing her sleep better - puppy was therefore over stimulated. We have mentioned it so much on this thread and it is really worth noting. My pup stopped biting us at about 11 weeks with a very very overexaggerated loud yelp and the realisation from me that I was overstimulating her since then I only give her half an hour of play in the garden plus a 30-40 minute walk a day - she is 22 weeks.
Well my day has been fun! Took Maggie to a friend of mine who has an acre for a garden, two labs one 9 months and one 3 years, chickens, swimming pool, fields next door, rabbit holes, rabbits, you name it. I have taken her before when she was about 12 weeks and I was so nervous as her dogs are really boisterous and I wouldn't let her off lead and eventually I asked her to put her dogs away. This time Maggie is so much older so she was off!!! It got a bit overwhelming for her at times particularly with the 3 year old joining in but playing with the 9 month old was hilarious, Maggie chased and chased and chased and the lab is gorgeous, really knew that she was so much bigger than Maggie and was very gentle.
On the way over we stopped at a pet store as I was completely out of food. They had harnesses in there and I was convinced we would have the same problem as before i.e. XSmall is too small and Small is too big, but no we found a harness to fit her which I am really pleased about as hopefully this will help with the lead work. Problem with it seems to be that she is now pulling but it makes her stand on her back legs instead of pulling and choking - she looks like a meerkat!!
I also took her swimming yesterday, we have a shallow stream near us that all the children play in during the summer. We took her in and she can walk a lot of it but had to swim some of it and she swam!! She didn't like it particularly as it was cold, she was shivering!