Dogs will surely test you and keeping hold of stuff is just one way in which she will test you. If you fail the tests, she will view you as being inferior as alpha and will take your place so you have to win every single time. In the wild, it is not in a wolfs best interest to be led by an alpha who isn't cut out for it so it's natural that they continually test them and take their place if they aren't good enough. You have to be firm. I have wrenched open a staffy x pitbulls teeth using my fingers in order to get it off our Mist before so you'll just have to do the same thing with your dog if she's not biting in response because it can be done and never ever allow her to win the test. If she continually loses, she'll stop being so persistent. The more you reinforce her belief that she is winning, the more testy she'll become and may even start to become a problem in other areas.

Don't be mistaken into thinking you have to be a bit soft on her just because she is new to the home. Dogs do not live in the past, they live in the present and you have to start as you mean to go on with them. It is known that a dog can be fully accustomed to it's new surroundings within 2 days and they usually are but humans are mistaken into thinking they need several weeks or even months to adjust. When they do finally start putting their foot down, the dog has long since decided it was higher in rank than them because they have been telling it so for the last several weeks or months and then they encounter serious problems because such a dog won't give up that position without at least some resistence.
When my dads border collie had pups and the two he kept were introduced to our Jess and Mist, Mist went straight into teaching them who was boss, pinning them down and snarling at them and even making them whimper and yelp. Jess just wandered off for a sniff around the garden and ignored them but would growl if they went up to her. It's funny how the pups couldn't get enough of our Mist though and perstered her despite her treatment towards them which looks cruel and harsh to us but it was important to allow her to do it. After a short time, the behaviour ceased and she settled down...pups knowing where they stood in the pecking order. So, if you look at how dogs behave with each other, you don't see them being soft for a few weeks first, they are firm right from the start, even firmer than most humans could bring themselves to be. Dogs only understand their own language. You have to speak dog.

Try to keep small personal belongings like socks out of her reach to start with to cut down on these situations. Take all of her toys away from her and choose one and only let her play with it on your terms. Afterwards, you take that toy away and she has to live with it. She'll soon learn that if she comes into possession of anything and you approach, she has to submit that item to you. Thats what subordinates do naturally.