AITAH for not contributing towards a friends travel costs to visit me

Long time lurker, first time poster here.

To cut a long story short, our (M28 and F28) friend (F28) has been asking us to pay 2/3 of her petrol/train costs whenever she comes to visit us.

She will stay over one night - she doesn’t let us pay for her food etc despite offering, but will eat/drink small things in the house. Obviously she also showers, keeps heating on overnight etc. To be clear, I do not care about these costs or even have an idea what they add up to.

We’ve had a back and forth over this for a year now. Originally we paid, but we started feeling it just wasn’t right to be “billed” £10-20 each every time she came. We asked for it to stop, and she originally agreed, but the discussions over it just have not stopped. She’s saying it is totally normal for us to pay towards her petrol costs. We’ve never had this arrangement before.

Other potentially relevant facts:

1. As a couple we do earn more than her, but she is not in serious financial difficulty or anything. Her parents do help her out with money.

2. She mainly visits us because she’s only just moved out of her parent’s house/shared accommodation, and we have our own place. Now she has her own flat we have already booked to go and see her.

Genuinely don’t know now if we are being unreasonable. So what do you guys think?