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我母亲已年满80，指纹有磨损不容易取样，之前申请绿卡打指模时，就被叫去打了两次，都没取成指纹，最后让我到所在的县警察局给我母亲出了个无犯罪证明，才算是过了关，拿到了绿卡。

 我母亲现在人已在国内，这种情况我能不能跟移民局陈述要求取消打指模，或是改期？否则的话我母亲刚回到中国又得回来，太折腾了！
-She needs to conduct the fingerprinting even if she got the green card. But she of course can re-schedule the appointment. Just follow the instructions on the Biometrics Appointment Notice to request the appointment reschedule.

I have no idea why USCIS asked your mother to conduct the fingerprinting again after they issued the green card to her. Because she has been over 19 years old, she does not need the background check using the fingerprinting. The fingerprinting is just used for the green card production only.