Answer: There are a couple of fungal problems associated with chrysanthemums, and one causes flowers to die before they open. Since your plant is in a pot, it probably came from a greenhouse where air humidity is high (providing perfect conditions for fungal infections). On the other hand, the simple change of environment from nursery to your home may have set the plant back a bit. In either case, I'd snip the flowering stems down to remove the affected buds and to encourage healthy new stems to grow.
Hope your mum perks up soon!
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