How can one please a deceased grandmother who might not forgive her grandson who did not visit her often and was unable to attend her burial?

If you have been remiss in maintaining ties with your grandmother, then you must seek forgiveness (istighfar). As for your grandmother, frequently supplicate for her and give charity on her behalf. Every act of devotion whose reward you dedicate to her will benefit her. The best way you can benefit her is by frequently supplicating for her forgiveness and mercy.