It's actually hard to understand.
forget (present) -- forgot (past); forgive (present) -- forgave (past)
You have both present and past forms in the one sentence, so I don't know what you mean to say. Did this actually happen? Also, "very difficult" may or may not fit the sentence, based on the first part.
Here are some suggestions:
I forgot about it and forgave her. It was very difficult for me.
To forget and then forgive her is very difficult. (Better: To forgive her and forget is very difficult.)
I found forgetting about it and forgiving her very difficult.
The English expression is "forgive and forget", in that order.