In real terms we knew her sources came from there though, because they had to. And if she wasn't speaking to them then she wasn't doing her job properly. So Cummings being revealed as a source isn't an actual problem for her, at all. She can literally just say "yes I spoke to Cummings, because I'm supposed to speak to Cummings".
The repetition without challenging part is the problem. And if Cummings said that's what she had been doing in exchange for information then that would be a huge issue. But he didn't, which is why I was surprised by the idea that she's been dropped in it. It's something she can very comfortably brush off.