My 4-month old squirms all the time when breastfeeding. She wriggles, flails her arms and legs (sometimes quite violently), and rubs at her face. I'm finding it difficult to keep her latched on. Why is she doing this and should I try to pin her arms down when nursing?

I think she is distracted so give her something to play with or sing to her while nursing. You can try to get a necklace with big beads that she can hold on to, distract her fingers. Something like this. There's also those silicon types which you can use for teething next time. You can definitely find those necklaces in Carousell.