With 300 TP and 2 BA flights already, DXB-LHR-YYX in PE on BA will give 360 more TP and 4 BA flights, so she will end up with 660 TP and 6 BA flights, comfortably crossing the threshold for Silver. Doing that trip in Y would still get the 4 flights, but at most 280 TP, leaving her 20 TP short of Silver.