She left the web, she left the loom, She made three paces through the room, (lines 109-110)
This is the sacrifice she makes for Lancelot and love. At least we think so. Is there any way to be sure that's why she defies the curse? Not as far as we can tell. She sees Lancelot and then she goes to the window. The events are really close, but neither she nor the speaker says a word about her falling in love. This is a pretty dramatic poem, but it also knows how to slow down when it need to, to keep things subtle instead of hitting you over the head with them. The love plot is here, but it simmers under the surface.
He said, "She has a lovely face; God in his mercy lend her grace, (lines 169-70)
Is Lancelot falling in love here too? It doesn't quite seem like that. It would be nice if he'd fall for her completely, but we just don't see it here. He acknowledges that she's pretty, but was that worth dying for? Still, there's a hint here, a little possibility that he understands what she's done for him. Not enough to take away the tragedy of the ending, but still, it's something.