I read your above added, 1) 49 days or 52 days? I would rather not to stuck with a concrete answer. But it's important to understand the significance of number. 49=7x7, 7 is an important number, we have 7 days a week, 7 colors in the rainbow... 7 is a number for a cycle. In the TTBoD you will find that every 7 days a more significant change. There is another sutra 《佛說入胎經》 which described how the embryo developed inside the womb, also in a 7 days cycle. And for female body, 7 years is a major cycle too, in general, eg, 7x2=14 a girl reached puberty, 7x7=49 a woman had menopause. And 3 is another number for a cycle. It is not easy to determine when exactly a person has left the body been in the Bardo stage. The doctor said heartbeat ceased means deceased, or breathe stopped, but some culture waited until the body is cold, the TTBoD said when the yellow fluid oozed from the body, etc. Thus 52 maybe is a safer indication since normal people do not have the ability to reach and communicate with the one already deceased to confirm when the cycle of leaving the body complete.
2) To "reach" a departed loved one after the Bardo: In Mahayana practice, many Buddhist Monasteries have a place to lit light (candle) for the departed, with his/her name on it. This could be for 1 day, 3 days, 7 days, or 49 days. The other way is to chant the mantra or sutra, and tranferred the merit to the departed. These are more ritualistic. Or to give away/ donate in the name of the departed, or his/her possessions, will add merit. However, in the buddhist teaching, everything is interconnected a thought with feeling is sort of energy, your thinking (blessing) directed to your grandmother will have effect on her, no matter whatever/ wherever she is.
Because the Buddhist view is that we have many deaths and rebirths in eons of kalpas therefore everyone could once be our father and mother, daughter and son, we should have compassion to all, and let go once a kinship ended. It is respectable you cared much about your grandma, however, after you have done all you know and can, that's the best of all.