J.M.
First, take a deep breath and try to relax and if possible, abandon your guilt. There are some things in life you are not going to be able to control and the sooner you recognize those things, the better you'll feel and the more energy you'll have to spend on those things you CAN control.
Is there a way you can change up somethings about your work situation? For example, can you ask about flex time where you get into the office very early, but are then home earlier so you have evenings with your daughter? Or, can you arrange to telecommute one or two days a week from your home?
If there is no flexibility at your job, have you considered looking for a job that is closer to home to significantly reduce the commute?
The other thing that will help will be to talk calmly with your husband. Let him know that you understand the pressures he's under and that you also need some more help when it comes to things around the house/your daughter. You'll need to be specific though -- outline exactly WHAT you need help with. If you just say, "honey, I need more help," he won't know where to start or how to help you and you'll end up frustrated that he's not helping.
Are there things you can simplify? Think about those things you "have to do" before bed vs. those you'd "like to get done" before bed. Are your expectations realistic given circumstances or do you need to take a long, hard look and let some things go, knowing that most parents don't have the neatest house? Can some things be moved to the weekends when you're home and more calm?
Some things that come to mind -- I find that doing laundry throughout the week makes it less daunting of a task in that I can toss in a load before work and move it to the dryer when I get home. I don't bother folding one load at a time - otherwise I'd feel as if I was always folding laundry. Rather, I wait until there are 2-3 or more loads of clothes and then sit down and knock it out at once. Perhaps for you, the folding is a husband thing or a weekend job.
Meals -- if you have some extra time on the weekends, make a meal and double or even triple the recipe. That way you have plenty to freeze one for another time and another for lunches (as you clean up the dishes, sort out your lunches right then and there so all you have to do is grab a container in the morning.) Same with salads -- if you eat them throughout the week, spend some time cutting everything up at once and assemble a few day's worth so all you have to do in the morning is add dressing - or see if you can store a bottle in the office fridge.
Perhaps along these same lines, start thinking about and prepping things you'd like to see your daughter eat. If you think she needs more veggies, steam up a big batch and put them in small containers where they need to simply be re-heated at mealtime. More fruit? There are plenty of them that can be cut/prepped ahead of time.
You mention she's a bad eater. How? Find out what your mom is making for her and realize that some kids are simply picky. I wouldn't focus too much on percentile - if your pediatrician is happy with her weight and development, give yourself a break and remember, toddler nutrition is to be measured by the week, not the day as we all know there are some days when they eat like champs and others when they simply won't touch their food no matter what is offered to them.
Would you be comfortable sending prepared snacks/meals for her when others watch her? Then you'd have some control over the things she receives.
Diaper rash -- what I've learned the hard way is that if my son has bad diaper rash, it's time to get a good pack of dipaers (pampers) and change him every hour to two hours until it clears up - even if it's a dry, clean diaper. The cheap diapers don't seem to wick away the moisture as well as the good ones. If it's a bad rash, invest in the good diapers (pampers) until it's gone and request that she be changes more often than she is.
Naked time works wonders as well as they have a chance to air out. If you don't think your mom or in-laws would be able to help in this area, then make time on the weekends for a few minutes (5-10 can make a huge difference in the condition of their little bottoms) each weekend day and maybe one or two week nights to run in the backyard free. (Plus, she'll LOVE it which in turn will help make you happy.)
Deal with mail twice a week -- put it in a spot where it'll be safe until you can get to it and then open it at once.
Housecleaning: see if you can figure out what takes the longest. Is it dusting where you have a lot on display? If so, give yourself a break and pack some of it away for a few months (see if you miss it - you may be surprised) that way surfaces are clear and require a quick dust vs. an in-depth clean everything on the shelf kind of cleaning.
If you can, clean the bathroom on the way out of the shower - really bathrooms don't take that long. Especially if the counters are kept clear. Having said that, minimize clutter where-ever you can - baskets on bookshelves are wonderful for collecting stuff and providing peace of mind when you walk in the door.
Make a list of those things that seem to stress you out the most and then start figuring out ways to fix them.
Relax. You're going to have another baby and life is just going to get more crazy. Spend some time now looking at ways to change some of the things that you can and that bother you most. It's going to be a process and not something you'll accomplish overnight.
If you can, sneak in a "sick day" where you feel perfectly healthy. Send your daughter to your mom's as you normally would and spend a few minutes on you. Sit and have a cup of coffee while you game plan what you can do. Spend a few hours accomplishing some of those changes and then go pick up your daughter for a fun-filled afternoon. You'll feel better because you've accomplished something and she'll love the extra time with you which will also be a feel-good for you.
Hugs to you and congrats on the upcomming baby.