Yikes! I don't think there's a lot you can do, behavior-wise, in three weeks, but you can prevent something bad from happening by taking her on walks during slower hours, keeping her sequestered in another area when new people come over the house, and picking up a Gentle Leader head harness
, which will give you more control if she tries to lunge at someone. I'd also say, avoid walking near folks. If you're walking and you see someone approaching, duck down a side road with her, or pull her off to the side and have her sit for a cookie until the person passes.
Maybe the more she's getting to know you, the more protective she's getting?