HI,
I think she is too young to understand that she should not put thumb in her mouth or to take any directions for you or get what you mean. So, all you can do right now is take out her thumb whenever she puts in her mouth. Keep doing it and give her a hanky to hold or a rattler to play with.
Generally, babies suck their thumb or fingers is because they are born with it. This is how they fill their tummy by sucking, so it is a kind of reflex action for them. Sucking necessarily doesn't mean that baby is hungry. Babies also suck their thumb because it calms them down. This is what pacifiers do. By the age of 2 or 3, she will on her own leave sucking the thumb, or as she grows you can give her other comfort objects, like her favourite toy, so that she is engaged playing with it.
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