Awww, she looks so sweet! Bless your heart for taking her in - I'm sure she'll be so much happier with someone who can pay attention to her and give her the love she needs. You sound like you're already wrapped around her paw
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Yeah, I'd probably just cut those mats out if they're too close to the skin for combing out. She may look choppy/funny for a bit, but it will grow out in time. Mine are very sensitive to brushing around the face too, so I'm not surprised yours is.
As far as food, I'm not sure of the amount bc you didn't mention her weight...but as long as you're feeding close to the guidelines on the bag of food and her body condition feels right (not too fat, not too thin), you should be fine.
WELCOME TO YT!!!