She is not ready for a new relationship. She still loves her
ex.
Are you confident that you will be able to let her forget her
feelings for her ex?
If she needs a long time to forget her ex, are you ready to stay
with her, despite being under the shadow of her ex?
These are questions you need to ask yourself. If you're confident
you can do both of them, then yes, fight for your love.
If you aren't confident, stay as a friend first. Heartbroken girls
are fragile, and vulnerable. A hasty entrance, without
consideration of your own determination, will only harm your
chances. On the other hand, this is also the period where you can
make the greatest impact on her.