Of course you aren't a bad Mum.

One thing I was told that stuck with me when I was pregnant with DD was this. Remember that #1 has been just that for a long while #1. Before your DS came along your DD got what she wanted, when she wanted it....Now all of a sudden, she has to wait. She has to entertain herself a bit. She has to share the biggest most important person in her life. YOU. Go easy on yourself, and her. She is little and she cannot understand as well as you the demands of your DS. She doesn't get why, so do try and cut her some slack (within reason of course). Your DS will be #2 for ever, he will never know the difference so putting him down a little more, or finding ways to get him sleeping without too much settling by you might help. He will always know that he has to share you with DD....he has from his day dot!

With my two, I have issues at times (as we all do) but I do try hard to spend as much one on one time with my DS as possible. I put my DD to sleep in her pram, so I get DS to help me push her around...and while we do, we talk. He is helping and he loves it (granted he is older than your DD but he has had me alone for longer too!) When I'm changing my DD on her change table, DS stands in her cot and watches and we talk and giggle at DD while she's being changed. He even got a toy chicken and decided it was HIS baby and puts a nappy on it when I'm changing DD, and baths the chicken, and wraps it in a towel!

Just try and find a little bit of tiime for your DD, and maybe mellow out the bedtime routine a little too. Like everyone else before me has said 'this too shall pass'