Help me understand the engine evaluation of this position.

This is a recent blitz game between myself and my girlfriend, both rated in the 1400s on Lichess. She often creates these kind of formations, with her pawns advanced by a single square and with slower development. I try to push forward with developing my pieces to punish this, but I rarely manage to break her defence.

My specific question is about how the engine has evaluated this position. It rates the current board state as +1.8. The recommended move is e5, shown in blue, which moves the evaluation to +1.7, and results in a trade of pawns. In the actual game I played b4 (in green), followed by her playing ...Bb7 (red). This looks like a very similar situation, but now when I look at pushing the e pawn, it drops the evaluation from +1.3 to 0.0, and I'm not sure why.

Can anyone help me with analysing these kind of opening situations with opposing lines of pawns? I notice that the Bishop is now pointing at my Knight, but this is still defended by the Queen, so I can't see how it results in such a dramatic drop in evaluation. What are the general principles I should focus on in these cases? Thanks.

HUH?