Getting cat to use scratching post?

I'm the one who has considered bringing in a stray, and did not want
to declaw her.

Before I commit to letting her in full time, I've been letting her in
for short periods (an hour or so), supervised.

I bought a sisal scratching post, and one of those cardboard
horizontal scratching pads.

When she comes in, she goes straight for my recliner and starts
scratching it.

I gently pick her up and set her next to the post.
She hasn't used it once.

But 5 minutes later, she goes back and scratches the chair.

I can't let her live inside until I can trust her.
How do I train her to scratch the post?