How to stop a cat going up the chimney?

[tostaky]

We’ve just got a 6 years ild cat two days ago. This morning, i could not find her but my living room floor was full of sooty paws. When i brought some food out, she came down the chimney!!
ive looked at chimney sheep but if i look at my chimney, i can see there is a space on each side where she could be quite comfy, before the actual chimney shaft (whete the chimney sheep or balloon would go).
if you have a cat, how do you manage this? We want to be able to ise our chimney from time to time too so not looking to block it off permanently!
many thanks

Thank you all - i do have a fireguard but she can move it easily as it is fairly light.
she also has a little cat den thing and she is in it at the moment. I need to find some cardboard boxes because she peed in the one i gave her the first day!
Thanks for your reassuring comments, i do hope she will settle soon enough so she wont need the chimney!