After watching the scene again, I can see how Molly came off as being a jerk on the phone, although I don't think she was trying to be one. She clearly thought something was up if the headliner dropped suddenly, but Issa was so rushed and cagey and didn't explain anything else. And honestly, I've been the Issa in this situation, where you don't want to explain the problem, you just want it fixed. Because it means admitting the part where you messed up, if you actually did. No matter what, it's embarrassing. I don't think Issa wanted to ask for Molly's help anyway. Molly was the least supportive of her friends when it came to the block party.
Still, Molly's a lawyer, so the prying and by-the-book questions made sense. She may have thought she could help Issa somehow, if there was a legal situation involved. But Issa cut Molly off and asked her to work her magic by speaking to Andrew. Molly was probably offended that anything she had to offer was irrelevant and Issa only needed a hook up. Again, perspective. Molly sees Issa as coming to her for help when Issa blew off the important talk they really needed, Issa sees Molly as lecturing her again for her mistakes.
I just realized that any growth Molly is showing is only with Andrew. She's making an effort to communicate, be more flexible, and less judgmental. But she needs to do that with Issa, too. And possibly her family.