I was still feeding our ds at night at 9mo. We did gradually reduce it, up to that point he just wouldn't accept my dh because feeding to sleep was his comfort and made him feel safe (not that he didn't feel safe with my dh - he was obsessed with dh during the day, but bf will naturally create a soothing effect and you make more milk at night).
We started by my dh going in when ds cried at night and he'd try to settle, then if that didn't work after a few minutes I'd go in and feed him. Gradually he started to accept dh and actually now dh does most of the night wake ups because he can resettle ds faster as he will just look to feed if i go in. So I'd also say be careful what you wish for there!
I do think these things are best left to settle themselves as naturally as possible unless it's no longer manageable for the parents. Some people swear by sleep training (and I totally get why) but also many people worry about the effects of it on a child and it never quite felt right to me. Children are biologically programed to want to be near their parents, especially a parent who is also a source of food and comfort through milk. So to me it felt right to wait until ds felt ready to be in his cot and every child is different. It would be worth chatting this through with your partner as she might just be thinking differently about this to you.
For what it's worth, most of the people I know who breastfed had a similar set up to you and co sleeping is proven to promote successful breastfeeding and let breastfeeding mums get more sleep than they would otherwise. Breastfeeding is recommended by WHO until at least 2 years of age. So while yes, loads of people decide its time to wean before 1, there's nothing abnormal about going past it. It's tough on a relationship but it is normal.
Ds is 16 months now and for the most part we have got him sleeping all night in his cot in his room but if he's having an unsettled night we will always revert back to dh in the spare bed/sofa and ds in bed with me because in my mind it's more dangerous for me to fall asleep in an armchair with ds than it is in a safe sleep position in bed. If you're both exhausted then that's an important factor to consider.
I would also say, breastfeeding is super emotional sometimes... I struggled massively at the start and was really scared about my supply dropping and worried a lot about having to stop before we were ready to. I was really anxious about dropping night feeds because I was really scared about the impact on my supply. So it's very possible that your partner is having similar worries. Its probably feeling like a big part of her bond with your baby and she might just not be ready to let that go yet.
I think you need to be patient and what I would do is seriously consider getting a larger mattress/floor bed so you can sleep in with them. I'd also speak to your partner about ways you can invest in your relationship and closeness as a couple without your wee one present through a date night or getting someone to babysit for a few hours.