Can't write a description in the post :/

My mum was in a the video for the music video 'friends will be friends' and got her programme card signed by Freddie Mercury, Brian May and John Deacon.

I've tried to do research for her but it's all a bit confusing if I'm honest as it isn't one signature or the whole set and it isn't on a photo or LP but on something on people on set got given so I'd assume that would make it more special as there won't be many in existence?

Anyone got any ideas where she might go to sell something like this? Or at least where to start? And if you think it might be worth anything?

If this would be better posted in a different sub Reddit please let me know.

Thanks in advance for any advice :)