Sorry, haven't time to read the whole thread, I've a 21 month old and a 2 month old to get out of the house! I just wanted to say that I felt terrible when DD was tiny. I was overwhelmed, scared, and totally out of my depth. And I felt totally alone in all of it because everyone kept telling me how wonderful the whole thing was, and all I could think was 'really? how?!'. But DS was conceived deliberately so obviously thing improved immensely 
Firstly, hell yes, you can force her to sleep. That was my main problem with DD - she wouldn't sleep during the day. By lunchtime she'd be cranky and by the time DH got home I'd be in tears myself, every single night. Then I started following the Baby Whisperer's routines with her, and made her sleep, and both she and I were much more content. The thing is, when they're that tiny, they don't know what they need. You're the adult, and if you know she needs sleep, you've got to persuade her to do it! I'm not talking about anything involving crying - my solution was to hold her for naps 3 times a day till she was 7 months old, at which point she accepted the cot as an alternative. She learned fast that my arms, and the dodi, meant naptime, and after a couple of days, she'd switch off like a light for a solid two hours when I sat down with her. Bliss : )
Secondly, try to hang onto the thought that everything's just a phase. You're heading into the four month sleep regression at the moment. It's tough, but it ends. Do whatever you need to to get through it, and pick up the pieces afterwards when things are less fraught.
Finally, remember, it really does improve. The more they respond to you and interact with you, the more fulfilling the whole thing becomes. Toddlers are brilliant : )
Sorry for blathering on so much 
Seriously, get her to sleep during the day. I'd bet my right arm that that'll be what turns your days around.