Can my niece represent me in civil litigation?

If the niece obtains the power of attorney from her uncle, she can of course represent her in court. Because according to Article 58 of the Civil Procedure Law of People's Republic of China (PRC):

Article 58 A party or legal representative may entrust one or two persons as agents ad litem.

The following persons may be entrusted as agents ad litem:

(1) Lawyers and grassroots legal service workers;

(2) Close relatives or staff members of the parties concerned;

(three) citizens recommended by the community, units and relevant social groups where the parties are located.