Asking my 12 year old sister to be bridesmaid?

I did these for mine, they ae cheap enough to get and I got a £1 frame from Asda. they all loved them and the younger ones have them in their bedrooms.

Personalised Will You Be My Bridesmaid, Maid of Honour, Flower Girl, Bridal Party Gifts for Sister - Will You Be Presents for Wedding Party - A5, A4 Prints and Frames - 18mm Wooden Blocks : Amazon.co.uk: Handmade Products

Or if you thing that is a bit young i got this for the older ones, is difficult as 12 is that middle age group, but this one could work and is a bit of fun

Will You Be Bridesmaid, Maid of Honour, Matron of Honour PERSONALISED Gifts for Her - Funny Will You Be My Maid of Honour, Bridesmaid Proposal - Gifts from the Bride and Groom for Sister, Friends : Amazon.co.uk: Handmade Products

There are loads of 'will you help me tie the knot?' bracelets and necklaces out there - maybe one of those? You can get them for under £10 (in many cases under £5) and they are the kind of thing that could be worn by an adult or a 12 year old. At that age, it's nice to have something 'grownup' sometimes.

E.g. https://www.etsy.com/uk/listing/1139309756/i-cannot-tie-the-knot-without-will-you?click_key=384f5d91099c5a09eb22908969591417913bbaa4%3A1139309756&click_sum=0694962a&ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=will+you+be+my+bridesmaid+bracelet&ref=sr_gallery-1-12&organic_search_click=1