all typical and very normal behavior. a 7 wk old pup doesn't know bite inhibition yet. 7 wks is IMO too soon to leave the litter, so now YOU will need to teach her how to play appropriately.
when she bites - let out a loud YELP (just as another pup would do) and get up and walk away. ignore the pup. play is over when biting happens. she will learn, but it will take time, and repetition.
yelp and leave. yelp and leave.
if she is coming after you (or pant legs) gently scoop her up (do not say a word) and place her in a safe spot - i.e. a crate, or a confined area (x-pen) or a gated room. leave her for a min or 2, and let her out when she is NOT whining.
no need to hold her muzzle at all. it may have an opposite effect and make her scared of you, or scared of you touching her head which could lead to problems down the road.
try the yelp! and ignore first. try gentle and calm "time outs". praise her good behavior. give rewards for not biting and only using toys. and sign up for a puppy behavior class for socializing skills. it's worth every penny IMO.