Strange High Chair Kicking Habits

[IB1988]

This is a bit of an odd one but my daughter is 16 months old and is hypermobile in her joints. Almost since we began weaning her, she's had a really strange habit of swinging and kicking her legs really really fast in her high chair. We've tried different high chairs but it hasn't helped.
It's almost like she's possessed and she won't focus on anything else. When we try and talk to her calmly or gently hold her legs to stop, it makes her cross and upset and she does it even more. It's not a gentle swing, it's incredibly rapid and crazed.

I wondered if anyone has had a similar experience. The habit seems to have got worse and it sometimes stops her from eating most of her food or she falls asleep in her chair because she's so tired from the exercise.

Thanks

I've never come across this before.

Have you tried telling her (firmly) to stop?

Have you tried a booster seat on a big seat so her feet are on 'solid ground'? So she's sitting up at the table with you?

@NuffSaidSam thanks for your reply. Yes we've tried a firm approach as well as a softly spoken one! We have a Baby Bjorn high chair at home which has a foot rest and she's sometimes a bit better in that than in the one at her grannie's house where her feet just dangle. Booster seat is a good idea - do you know any good brands?

Thanks!