The 22-year-old remains critical after she was discovered unresponsive in her bathtub two months ago.
"There's not a great deal of hope," the 81-year-old, who confirmed that Bobbi was recently relocated from her Atlanta hospital to a rehabilitation center, told New York's WBLS.
"I don't pray like that. I give it to God one time, because I know he's able, and I cannot change a thing," Houston explained.
"So I'm asking everyone to pray to the Lord, who we know can do something about it. If he works a miracle, thank God. If it happens the other way, I'm all right."