She played four seasons at Cornell University and was selected second overall in the 2012 CWHL Draft by the Calgary Inferno.

[1] Johnston (and future Cornell teammate Catherine White) represented Ontario at the 2007 Canada Winter Games.

In the gold medal match versus Manitoba, Johnston and White each had one goal and two assists, as Ontario won by a score of 6–3 and finished the tournament undefeated.

[3] Johnston was Cornell's first player to be named first-team ECAC Hockey and receive rookie of the year honours.

Johnston won two gold medals with the National Women's Under-22 Team at the Air Canada Cup.

Rebecca made her debut at the 2008 IIHF World Women's Championship,[1] playing in all five games as Canada won silver.

[1] Contested at Ottawa's Canadian Tire Centre, she scored twice in an 8–3 victory over Les Canadiennes de Montreal.