Food advice/question

My dog had surgery to remove her anal glands (im sorry i dont know exact terminology) and is having a hard time pooping. I'm assuming the poop is too hard and the pain she feels trying to push it out makes her quit trying so its just small pieces that come out and end up falling while she walks. Has anyone had similar issues? What can I feed her to make the stool softer so she can go to the bathroom all at once? Its been over 20 days since surgery. Sorry if I was too explicit but I don't want her to suffer with this anymore