Mucinex for 3yo?

I posted yesterday that my daughter has a cold. Today I had to drop her off with my mil and when I went to pick her up, she let me know that my daughter was experiencing a bit of pain when coughing so she gave her mucinex for children (without my knowledge). I’ve heard a lot of bad things on cough syrup but was wanting to know the opinions of you ladies on here. Is it ok? Should I purchase it for her? Pls let me know!

@Al that’s exactly what I thought. It almost felt like she was trying to make me feel guilty. I let her know doctors don’t recommend cough syrup as the amount needed to make any kind of affect on small children can potentially be dangerous and her respond was not to trust doctors that they won’t give me anything for her and that it’s not fair for her to suffer just because I choose to believe what doctors say. It’s frustrating since I unfortunately don’t have any other childcare for Thursdays and can’t take them off as we need the money.