Angela likes to think she's the first person who saw it. It's in the way Jane talks about Maura when she's not around, and in the way Jane looks at Maura when she thinks that the good doctor, and everyone else, isn't looking. Her face is so open it reminds Angela of when Jane was a child, there is so much innocent emotion that Angela doesn't even know how to broach the subject.
So she doesn't, she's just happy to sit there and watch the pair of them, giving the occasional push when she thinks they need it, and sitting around and listening to them both when a relationship ends. She doesn't understand how they can't see it, but they are both completely oblivious to the attraction between them.
As much as she jokes about trying to set her daughter up with someone, there is a part of her that hopes one day Jane and Maura will become the lovely couple she thinks they'd be. For now, she's just happy to sit back, watching and waiting for them to realise what everyone else can already see.