If the pup is nervous because it is her inherited nature, then go very gently with her. If she is nervous because she wasn't sufficiently exposed to different people before she left the breeder, still go gently. Don't force people on her. And definitely don't flood her with new and frightening experiences at this age: it's far more likely to make her a lot worse. The desensitisation process must be very gradual, very gentle, and you only go as fast as the pup is capable of going. If you just stick her on a lead and walk her amongst loads of people she may well never get over it. 13 weeks is a difficult time for a lot of puppies. Fearful experiences at this age can mark a dog for life.
Concentrate on building a strong bond with her, get her total trust. Once she looks to you for protection and support only then can you start to expose her to new and scary things. Never push it. Each new step she takes must be totally within her comfort zone, and you must always be there to support her. Don't let strangers go rushing up to her saying crap like 'I'm used to dogs', and don't try and do any training at the moment either. Anything she experiences as negative will only put her back further. No telling off, no shouting, no making her sit etc etc.
I've had one or two lurchers like her, and they've turned out the most rewarding animals, but they must be allowed to come on at their own pace, which doesn't mean that you keep her shut away, just that you watch and read the pup and let her tell you when she's ready for the next step. For example: get her sitting/standing by your feet when you talk to a new person. Don't let that person make eye contact with her or approach her in any way. If possible, get the person to sit down near you, and chat away. If you want the pup to trust other people, apart from yourself, then get the person to offer her a titbit. Personally I wouldn't do that: far too many thieves about these days. If you just want her to be confident and comfortable around people in general, just stop and chat with as many people as you can whilst you walk her, but don't try and force her to go near them, and tell them what you are doing and why.
Hope this helps.