If she values a specific ring that's out of budget more than holy matrimony with you, maybe it's time to cut your losses if she continues to insist. I value my partner's companionship more than a ring that can be lost or damaged.

£1000 is not outrageous for a wedding ring, but it depends on your financial needs, as well as how insistent she is about other things with the wedding (like location, dress, food, etc.). If she's willing to cut back on other things for the ring to fit the budget, and you're okay with those too, go for it. But if at this point she's insistent on breaking your budget for things only she wants already at wedding time, jump ship now. I guarantee you will fight and argue about money your whole marriage if this is the case now. It's hard enough when you're mostly aligned, and my wife and I's biggest arguments have been when she wanted to buy something beyond our budget and I didn't. (sometimes it's the husband that is the spendy one too). If she's making ultimatums at this point and it's not something you'll be okay with your entire marriage - get out before tying that knot, because you'll be tying an albatross around your neck.