First of all, I'm sorry that mom is accusing you of "pressuring and forcing her with pear juice". Sheesh! That is the healthy way to deal with it! Second, it seems normal that if she was constipated, it would be followed by diarrhea. If the constipated stool is blocking the rest, then what comes after it will be over-processed. I think pear juice is a good start. Definitely make sure she's properly hydrated on a daily basis, not just when she complains of constipation. And, speaking as a mom of a chronically constipated child, it is normal for kids to have wacky bowels. Make sure her diet is fiber rich and cut back on binding foods like bananas, rice and too many carbs. The thing that's too bad is that kids get easily freaked out when it hurts, then they hold it and make it worse. It starts a bad cycle. I'd just make sure her diet is helping her and stay calm about it to help keep her calm. If she really is starting to have a problem being regular, talk to your pediatrician and ask about Miralax.
I also swear by Yo-Plus yogurt. It has probiotics for intestinal health, as well as 3 grams of fiber, which is about 1/3 of a toddler's daily recommended fiber intake (8-10 grams).
Good luck!