Littlejohn, who joined Women's Super League 2 side Crystal Palace in the summer, will now be out of action until after the winter break.
She will miss second-tier Palace's meeting with European champions Arsenal in the League Cup quarter-finals on December 19.
Littlejohn will also miss the FA Cup second round tie with Lewes, and three WSL2 matches against Birmingham, Bristol City and Sheffield United.
The veteran midfielder has said she "regretted" the incident with Wales international Cain.
"Obviously I regret letting my emotions spill over on the pitch," she said at a media conference with Republic of Ireland during the international break. "I'm quite an emotional person and player.
"That's not who I want to be on the pitch, so I will learn from it and move forward."
Republic of Ireland manager Carla Ward said Littlejohn had been subject to an "outpouring" of "disgusting" abuse after the incident.
"She is a human being," said Ward, who previously managed Littlejohn at Aston Villa and Birmingham City. "She's someone's daughter and sister. It's not OK.
"I look at Ruesha - and it's not just because I've got a long-standing relationship with her. Some of the stuff I've seen this week has been disgusting.
"She has acknowledged it was a moment that she deeply regrets.
"We're not talking about defending the incident here. We're talking about what follows and we need to do more to protect players."