I really struggled with breastfeeding and wasn't supported enough, so I ended up formula feeding DD from day 3 onwards.
I felt guilty for so long. It triggered postnatal depression, I became incredibly defensive, I was convinced that people were glaring at me every time I reached a bottle out in public. I was so ashamed.
Then one day I looked at DD who was (and is!) healthy and happy and clever, and felt so upset about the time I'd wasted feeling guilty and regretting it when I should have been enjoying my gorgeous DD and being proud of myself for all the other things I'd accomplished in the early days of motherhood.
Feeling guilty is totally natural, and be prepared for it to sneak up on you at random times, but please try not to beat yourself up. The way babies are fed is, in the grand scheme of things, utterly minuscule in determining their futures. You can't walk into a room of two-year-olds and point out which ones are formula fed and which ones are breastfed. They won't have to state it on university forms or job applications.
Every woman should be supported to breastfeed, but no woman should be made to feel bad if she is unable to, or chooses not to. Your daughter is healthy. She is happy. Her head probably smells amazing (can you tell how much I miss newborn head sniffs?
). That's all you need to tell you that you're doing a brilliant job, regardless of how you feed her.
DD is now three and the days of feeding are a distant memory. If I can get her to react positively to a meal that isn't pizza, it's a win. I don't think breastfeeding her would have made a jot of difference to that 
You're doing brilliantly. Congratulations on your baby 