Weir will compete at the Inter County Championships at Prestwold Hall in Loughborough on Saturday, which are acting as world trials for the under-20 age group.
To guarantee a spot on the plane to Kampala for the event on March 26, Weir needs to finish in the top three at Loughborough.
The remaining three places in the junior women’s team will be decided by a selection panel.
Weir did win the European Cross Country trials in Liverpool earlier in the season and was part of the Great Britain junior women’s squad that won team gold in Chia, Italy.
The University of Birmingham student finished 10th overall in the European Championships.
Weir also earned Great Britain international honours at the Great Edinburgh Cross Country and was selected to represent England at the Elgoibar International Cross Country in Spain, where she finished second.