Is losing over six stone in nine months realistic for a wedding?

[DoeIdea]

Friend is getting married at the start of may. She's obese currently at 20 stone/5'3 and has bought a dress that's gorgeous but is only a size 12. She's currently a size 26/28 for context and is adamant that she's going to lose enough weight to fit into it for her wedding. It's over six stone which seems a mad amount to lose in that time period.

I'm really worried that's not going to happen and she's going to be disappointed or frantic trying to find a new dress. I've been gently trying to get her to look at dresses that will fit but she's refusing.

Is it even possible to lose six stone plus in 9 months?

She's incredibly committed which is wonderful. Normally we meet up on a Sat morning for a coffee and cake but she had a gym class.

I'm really hoping it works out for her!

I am 5 ft 3. I’ve gone from 12 stone 3 to 9 stone 10 in 6 months, 2 of those months on WLI. I do not eat more than 1200 calories a day on any day ever, and often less. I don’t drink.
I’ve only dropped 2 ish dress sizes (was 16/18 before; now 12/14.
Now I’m probably a lot older than your friend, but this is going to be hard going and actually pretty miserable during a time when she should be excited and looking forward to things. I don’t doubt her commitment but also it would be rubbish if she felt a failure on her wedding day because she’d ‘only’ lost 4 stone….