Fear-aggressive young dog in my care?

I'm fairly new to Rover and dog-sitting but have owned dogs all my life and have sat for friends before. I recently did a M&G with a new client and although the pup was not overly outgoing, she seemed fairly content and happy. She seemed curious of my 3 dogs and my dogs seemed OK with her too. Fast-forward to boarding day. She's staying in my home for 15 days while her parents are out of the country. Within a couple of hours of her being in my house, I've been bitten twice when I tried to remove her leash. She's extremely fearful and anxious. So I'm giving her her own space with her belongings near her. I asked her owner to provide some pieces of clothing so she could keep their scent with her. However, I think she's starting to be possessive of her space and when I try to approach, she cowers and growls.

Any suggestions on how I can continue her stay? I don't think I'll be able to take her on walks because her collar just doesn't look secure and I fear she'll pull too much and possibly run away if she ends up getting out of her collar. She's quite young, only 10 months.

My husband just walked into the kitchen which is separated by a baby gate and she's currently in the office area close the kitchen (an open space) and she growled at him without him even being that close. I'm getting worried she won't let us near her at all now (where before she at least let us walk around her without issues).

Any thoughts are appreciated!!