WWYD

I think it's her party so wouldn't want to pay petrol.

I would reiterate you weree only going because her husband wasn't. Now he's available ask if you can back out.

I would probably say I'm not going if he is available.

IWG

Go, you might enjoy it, and you'll meet new people.
If you want to you could offer to share the cost of the petrol, but she invited you and would still have to pay if you didn't go!
A little gift for the hosts would be nice. What kind of party is it? Birthday, anniversary or what?
How about some pretty soaps or drawer scented paper? It's hard when you don't know them but you should ask your friend what kind of things they like, if they have hobbies or whatever?
It doesn't have to be a gift for the actual party reason, but something to leave for them to say thank you for inviting me/putting me up!
I think it could turn into a lovely girls outing kind of thing.

Do you know the relative? To be honest I would not want to go if they are all complete strangers and I'm struggling to see the point. If the husband of your friend doesn't want to go I would wonder why. I also would not like to have an overnight stay in the house of a stranger but then that is just me. I would prefer to stay in a nearby hotel (if I went at all!!)

Thank you for the replies.

I will go as I would be letting my friend down and relative is expecting me. I don’t know the relative but understand her husband finds them boring, hence the reason for him not going! However, I don’t want to spend a lot on something that I’m only the spare part at!
Good suggestion Ali08, soaps might just be the right thing to take. I looked at candles but anything nice costs a fortune.

At the risk of sounding negative, if the husband finds the relatives boring and no immediate family are going, I would not be expecting it to be a very enticing party to attend!

It's good of you to support your friend and nice of her to ask. You never know your friend might think you will be nice company to brighten the party.
I would take a bottle of Cava or Prosecco in a nice gift bag for the host.

If you have decided to go, I think some quality soaps are a nice gift.
Have a good time!

Just go and enjoy yourself .

Take some wine maybe some gourmet food -whatever you can afford .