All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
You should endeavor to supplicate Allah to forgive and have mercy upon your mother and you should not believe that she has apostated (became a non-Muslim) just because of what you have mentioned.
You should know that there are some conditions that must be met for declaring someone as a non-Muslim and there should also be no impediments for declaring one as such.
For example, there is the condition of knowledge that is contrary to ignorance; there is also the condition of intention that is contrary to error.
The person who is not in their right mind because of sickness may say things that one would not say when they are in sound health, and they are therefore, not held accountable as long as they are in that state.
In principle, a Muslim remains as a Muslim and he is not ruled to be a non-Muslim based on a doubt. So you should fear Allah and avoid these whispers on Takfeer (declaring someone as a non-Muslim) and strive to supplicate Allah to forgive and have mercy upon your mother, as a way of acting according to the Saying of Allah (which means): {…and say, "My Lord, have mercy upon them as they brought me up [when I was] small."} [Quran 17:24]
For more benefit, please refer to Fatwa 373009.
Allah knows best.