I think my zebra finch is going to lay an egg?

She keeps fluffing up and pushing like pushing the egg out her chest goes out really far (her pushing and every time she starts to do that pushing thing sh flys into rhe nest yes there is a male there she already has 1 egg so this will be her third (first egg got cracked I threw it out) so is she I am not sure because I didn't see her behavior when she laid the other eggs :/