Hi L. -
I agree that 1-month old babies sleep and eat with not too much of a schedule (or at least mine did). And he slept a lot as a newborn...then the catnapping began! So, I have certainly been there and read most sleep books out there. I did not try organizing his daytime sleep until he was 4 months old..and that may have been a little too late. He seemed to work out his day/night confusion on his own. He also has reflux.
One thing I did notice that was very helpful and very difficult with my little one was to work toward a routine, but I let him lead it and developed it around what worked best for him. Obviosuly, he is human, so some days he wasn't as hungry, others more hungry, but for the most part, I tried organize it. If you watch them and maybe even chart his days, it will help you to see the pattern. It will take a little time, but it should pay off in the long run. If she seems to be sleeping too much during the day and not at night, try stimulating her more in the day (but not too much, fine line there! Make sure she sees plenty of light (preferably daylight) and interact as much as possible (i know it is probably tough with another little one). At night, when you go in to feed/change be sure to stimulate as little as possible -- no bright lights. Do not interact...get in and get out! I know it sounds awful, but this will help her learn night is for sleep. I am not saying to do it in an uncompassionate way, but the idea is to meet the needs and nothing more (at night time only)! Daytime can be for all of the cuddles/kisses/love and playing. I hope this is coming off the right way...it sounds really harsh and I am really not harsh at all!!
Once she is older, her sleep will start to organize and lengthen. They say that in many babies this doesn;t happen for at least 3 months. But, if you start working toward it now, you will be that much farther ahead. If catnapping is still an issue at 4 months, e-mail me and I will give you all the pointers I have! For now, try and be patient and keep telling yourself "this too shall pass". I know it is tough when you are sleep deprived, but if we look at the owrld through a newbrons eyes, they are going through MUCH more than that!!!
Good luck.