Kid has anxiety about transition days - what helps?

My 8yo gets genuinely stressed on days she switches between houses. Won't eat much, gets clingy, complains about stomach aches. Ex says she's the same way at her place but I don't think she realizes how bad it is.

Has anyone dealt with this? I've tried talking to her about it, doing calm activities, but I think she just dreads the transition itself. Is this something a therapist could help with or am I making it a bigger deal than it is?