Tips for helping toddler poop

Hello, any advice on foods/drinks that will naturally help my toddler easily go for a poo? She’s quite fussy and seems constipated. She’s also fussy with what she eats so isn’t making this easy, I just hate seeing her getting distressed when trying to go for a poop and when I change her nappy there’s never anything much in it, just a small bit. I think she gets majorly anxious about going to the toilet as she’s had painful poos in the past and just holds it in now. It’s very distressing for everyone as she just seems so uncomfortable. TIA