我妈妈的绿卡已经在2020年过期。因为各种原因妈妈2015年离开美国以后就没有再来过美国。现在妈妈准备来美国定居，请问这种情况是不是最好先填写I-407放弃绿卡，然后重新申请？
-Yes.
I-407这个步骤是必须的吗？
-Yes. She needs to abandon the green card first because the system still shows her green card valid unless it is revoked by the IO at the port of entry when she uses it to enter US or by the immigration court/judge.
我准备用online application, 请问cover letter 怎么加上去？
-Not need cover letter. Read these links:
Abandonment of Status (Form I-407) - U.S. Embassy & Consulates in China (usembassy-china.org.cn)
How to Voluntarily Abandon Lawful Permanent Residence (a Green Card) | Nolo
没有找到可以加cover letter的地方。十分感谢。
