The verb loses its ending when you merge it with the pronoun.
- Esquecer ele = esquecê-lo
- Esquecer ela = esquecê-la
"Eu não posso esquece-la" means "I cannot forget her". So, "consigo" should give a sense of "managing to / being able to forget her" So, I think, "I just cannot forget her" is a better translation.
If I use "posso" instead of "consigo", how would that change the connotation of this sentence?