I am sorry to hear this sad story.
You can retain a lawyer to write the mother a letter indicating that while you hope this can be worked out outside the legal system you will have no hesitancy to seek a Court Order granting you liberal access rights if it cannot be as the best interests of the child requires your involvement in a meaningful way given your past care of her.
If the child is not safe you may also want to consider discussing applying for custody with the lawyer.
If she does not allow you to see the child after that you can seek a Court Order and it's likely the Court would grant you access and more in your case than in most based on these facts.
You can contact the Law Society and use their Lawyer Referral Service. You will be given the name of a lawyer and can consult with the lawyer and the first half hour will be free. The number is: 1-800-268-8326 or(NNN) NNN-NNNN(within the GTA)