EllieMcM - did you find any in Manchester/Chester area?! I to have the same problem, based by Warrington so easy reach to Liverpool, Manchester and Chester...my mum is coming from Ireland for a fewdays to come find her ideal outfit as she's not found anything in Ireland and my research isn't going too well for here either!
I have a Mother of the Bride shop in Worcestershire called Wedding Pearls.We currently have a few outfits up to a size 26 but I have loads more on order due in middle of April going up to a size UK30.
There is such a high demand for plus size special outfits yet all the designers shy away from this as it is not the standard market !! In addition the designers are very small made so you will need at least one size larger than your normal dress size.
My Mum went with Jacques Vert too. She broke with tradition and has gone with a fit and flare rather than shift dress. For me I want her to be comfortable and she loves it. It also came up a little big so having it in a size "lower" was a real confidence boost to her
I must admit I am having more fun finding bits for her than for me!
Take a look at the Bombshell Dress's that Milla Grace Brighton stock they go to a size 18 and there is something that these dresses to that are SUPER flattering! They are comfortable and easy to accessorise, also you can wear them again! Also you can shop and return online - http://www.millagrace.co.uk/designers/bombshell
I think you should make a special dress for her from a tailor or seamstress because I don't think you guys will be able to find a suitable ready-made outfit for her. My daughter is getting married next month and being the bride's mother, I really want to wear something special. I don't want your mother's experience to be ruined so do make an effort.
We have a shop orselves, ie www.thebridesmother.co.uk and have to say that the choices for large sizes are slim. Ann Balon is sort of old fashioned now. There are those sort of sizes from the likes of Cameron Blake and associated labels which are soft and floaty and much more fashionable than heavy lace. You just need to start looking WAY before the wedding date though as they are generally order only and can take up to 12 weeks to be delivered.
When we get someone visiting for larger than we can get our hands on we ALWAYS send them to Florentyna Dawn.
She is the epitome of elegance herself and she has the most delightful styles for larger ladies, mostly made in-house.
We do have a couple of collections which give us room for manoeuvre now. These are new Italian styles and they can be made to measure if needed that way, or mix and match in sizes where the body shapes is smaller on top than the bottom for instance.
Apart from that, the new styles coming to us are absolutely knockout.