Tbh I'm not sure if it is Vincent that she trying to protect them from, I mean she could potentially use it as a excuse but it come not long after Charlie told her Matthew had sat up and Roxy said something about it, I think she genuinely jealous of Roxy seeing Matthew's milestones and basically being his surrogate mother since she been in a coma, he now 5 months old a lot to miss.
Put that with Roxy's betrayal, she paranoid that Roxy's gonna try and take what her again, I'm not sure if she genuinely in love with Charlie but she just want to be a normal mother and have a family and not be divorced a second time.