5 month old pup start to show aggression

I have a 5 month old Golden Retriever girl. She is so, so sweet in most ways however has started to really test the boundaries and has started growling if we go near her when eating a bone and even started at the vet when he was checking her eyes the other day.

 

Tried many different things e.g. approaching with another tasty treat when eating her bone, loud no's etc. but nothing seems to be really hitting the point. She is fine with her normal food and I can feed her by hand, hand into her bowl etc no problem.

 

But she's behaving very differently than my previous goldens as they all tried this but a sharp 'no' and they'd have they're tail between their legs but it doesn't seem to bother her. They also only tried this a couple of times and learnt it wasn't acceptable. This isn't happening with her so don't think it's something she'll grow out of without some guidance.

 

She's well socialised, fine with other dogs and is actually is very submissive,gentle with them.  In the dog park she spends a lot of the time on her back and never challenges for a ball etc. So very converse to how she behaves with humans. She's a few rough edges but rest of training is going ok and she's pretty good on the lead etc. Goes on regular walks, I work at home so she has company.

 

I wan't to be able to nip the aggression in the bud asap but feel a bit out of my depth and don't want to make the situation worse by my own DIY methods. Thinking that maybe one on one training in my own home situation might be worth investing in rather than group training. What do you think? Has anyone worked with anyone they would recommend (live in south dublin)?

 

Thanks a mill for your help. S x