Most Helpful Girl
I don't believe she can just forget about you, considering the length of time you were together. Even if she ended it , she will think about you. Sometimes people's sadness is measured by the smile on there face.. not their tears. She may act like she doesn't care in front of people but inside the breakup will hurt her.
You were part of her life for so long. She doesn't have a " switch" to turn off all her memories, feelings and emotions. The only way she will know how to deal with the hurt of the breakup is to be with friends and act happy.
Regardless of why you both broke up or who ended it... it is still painful to see a chapter of your life close
Most Helpful Guy
No, I don't think it's possible to forget someone whom you were with for 4 years, and 4 years is not a short period and if the relationship was good and strong then it's not possible to forget that just like that, maybe she is showing that she has forgotten you and moved on but I am sure on the inside she still thinks of you, and remembers you.
On the other hand if your relationship wasn't strong, no strong feelings then it's possible for her to get over you easily otherwise not.