Cat flap

Question
We have had our cat for about 2 years, and she was an adult when we got her. She kicked up her litter tray a lot so we got her one with walls and a cat-flap. She uses it fine when the flap is off and there's an open entrance, but she won't use it with the cat-flap on. I have got her to go in it a couple of times by holding it open, and letting it close when she's inside. The first time she scratched around, panicking a bit, and the second time she scratched a bit but quite quickly found her way out. She still doesn't seem to make the connection though about how to get in. I think she relates it to the carrier we use to take her to the vet, which she hates.
She's a really bright cat, so I don't know if she's actually doing it out of protest, so I'm reluctant to take it off, in case that is giving in to her. Can you help me to find a way to make her understand how to use it, and let me know whether you think she does know how to use it, and is not using it just because she doesn't like it that way. She has never had a cat-flap leading to the outside, but we let her out a lot, as she is very much an outdoor cat.
Thanks for your help

Answer
Dear Erin

Thank you for your question.
Your are probably right to think your cat has a negative link to the cat litter flap and the carrier.  Plus it's something she is not use to and this can cause nervousness and fear.

You need to the link the cat flap being down with a something high rewarding to your cat, for example a treat or her favourite toy.  Every time she shows some interest to the flap, reward her with her treat.  Over time she will build her confidence up with the cat flap.

Kind Regards

Rochelle