"Perhaps I should just not do it at all. If I do, I guess it is still letting her have her cake and eat it to."
"I wasn't expecting anything with the lightbulbs. I was just going to do it to be nice. Nothing more. She asked for help on it and I agreed. I just haven't remembered to do it since she asked."
Wrong! You were expecting something even if you can't admit it to yourself (see above quote). Just changing a lightbulb for her isn't letting her cake eat. She asked and you said okay. End of story.
IMO I would change the bulb because you said you already said you would. Don't seem like an @$$ and then tell her you changed your mind.
A real man follows through on what he has promised regardless on who it is for.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.