Does anyone know of a treat that wont constipate my little Marley

She loves cheerios and cheese but she struggles to poop when i let her have some here and there. I let her have little bites and i mean LITTLE, of food that i eat that i know wont hurt her ( i.e. steak) when we cook out( about the size of 1/4 of a cheerio ). I have also noticed that she went nuts over the tomatoe sauce i let her lick off of my finger. I just dont want my baby almost doing a handstand because she is straining so hard to poop lol shes done that before.