“Sainthood” as used by the Church with respect to canonized saints means the Church has officially declared that a deceased person is certainly in Heaven. The person must be deceased.
In a broader sense, “saint” means any deceased soul who is in Heaven. Therefore, if your grandmother dies and eventually makes it to Heaven after some time in Purgatory, then when she reaches Heaven she is a saint. The Church will not be having a canonization ceremony for her because the Church restricts its official canonization to a very few holy people who lived exemplary lives on earth and have further shown their holiness through things such as martyrdom for the Faith and/or miracles performed through their intercession after death. But if Grandma is in heaven, she’s still a saint regardless of whether the Church has a ceremony and a feast day for her. There are millions of such unknown saints.
Note that in order to be a saint in any sense of the word, you have to be dead. Living people cannot be saints. We can refer to a person as being “holy” or even “saintly”, but until they are dead they still have free will and could be committing, or have the potential to be committing, all kinds of serious sins, so they cannot be a saint even if people might call them that, “oh he’s a living saint” etc.
“State of Grace” generally refers to living people, not dead people, and simply means that one is not in a state of mortal sin. Mortal sin is seen as severing the relationship with God. A person who has been to Confession within the past year as required by the Church, and has not committed any mortal sin, is in the state of grace. The state of grace is required to receive Holy Communion or get indulgences. Each time we go to Confession and get absolved, assuming we have made a sincere, honest confession and mentioned every mortal sin that we recall/ know we’ve committed, then we come out of the confessional in a state of grace. Many of us go to Confession frequently to make sure we maintain the state of grace.