Mira: the necessary evil......

I think it's fairly safe to say that Deanna is as averse to confronting people over matters of substance as anyone born a Patterson; no matter what indignity she might suffer, standing up for herself or her friends is more trouble than it's worth. This was especially noticeable during the big sham wedding; instead of simply explaining to Mira that if she didn't like Mike's friend Lawrence, she couldn't be part of her life anymore. Instead, she tried her damnedest to make the argument go away. As she would later on, all she ended up doing was impotently whining about how her mother wouldn't settle down and stop interfering. The odd thing about the dynamic between Mira and Deanna is why Deanna made such a point of wanting to keep Mira in her life despite so obviously despising her and regarding her as a domineering, selfish and petty obstruction. No matter what the stimulus, care was taken to make sure that Mira didn't simply wash her hands of her and let her do whatever she wanted. It's not just Deanna's need to not be confrontational when it actually matters that explains it; my guess is that she needs to have her arch-enemy mother hanging around to blame for all her troubles. If Mira's "bad" influence wasn't there, Dee might just have to accept personal responsibility for her problems and she just can't do that.