My girlfriend (27f) expects me (29m) to change my mind about going on a cruise next year since she doesn’t want to go on one

One type of holiday I've wanted to do for quite a while is a cruise. I have been working in my current job for 3 years and there have been a lot of exams with work to fully qualify. I found out last month that I’d fully qualified so I thought it was the perfect time to treat myself to a cruise.

My girlfriend has always said she'd never go on one. She doesn't like the idea of being out at sea and just said it's not the type of holiday she'd enjoy. I started looking at cruises available from the UK for next year to see what my options are and to price it up.

I mentioned this to my girlfriend and she asked why I was thinking about a cruise. I said because she knows I have always wanted to go on one and that it would be nice to treat myself for finishing exams.

She asked what about our holiday next year. I said we'd still be able to go on one but it would either be a bit later/earlier than usual and will likely be a night or two shorter.

I mentioned that she's welcome to join me on the cruise but she refused. She said it's not fair that our holiday has to suffer just so I can go away.

I pointed out it's a one off to celebrate my achievement and that it's not going to be a regular thing and our trip is only going to be a night or two shorter.

She just said that our holiday shouldn't be any shorter and that I'm wrong and selfish for prioritising the cruise.

Does anyone have any advice about how best to approach this or have any other views on it?

Tl;dr I started looking at going on a cruise next year to celebrate my achievements. My gf doesn’t want to go on a cruise and is expecting ring me not to go since it’ll mean our holiday together would be slightly shorter.