Old Chinese brass objects hold most value if they are old. There are tons of overvalued pieces of Chinese brass offered on ebay and other online sites. Many sellers refer to their wares as "rare" when they are not. Also there are many reproductions of antique brass that can be very pretty. An artificial patina can be added to new brass by using common household chemicals. According to some experts, most of the antique Chinese brass offered online is fake.
Older brass may show some wear in points of frequent contact, such as edges and handles.
Look for a mark stamped on or near the bottom of the piece. Draw the mark or take a photograph. You can then research the marks on websites like Kovels, Marks4Silver, or Antiquemarks. You can also comparison shop on Artifact.com or Sotheby's.com.
If you know a reputable antique dealer, take the brass to them and see what they will offer or if they will do an evaluation. If some appears to be very valuable you can find an appraiser.
I am a big thrift shop fan and often see Chinese brass pieces. It was popular in the 1970s. Everyone had trays, vases, and little figurines that they purchased on the cheap.
How you determine how to sell your mother's brass is up to you.