I agree with some of the responses that "bribery will get you anywhere" but at the same time, she needs to feel the accomplishment of being a "big girl." You have a 4 yr old boy and he is a "big boy." If you let him do "big boy" stuff and your daughter sees that it may encourage her by telling her, "oh, I am sorry, you can only do that if you are a big girl and would potty ALL the time...at day care AND home and not have accidents...once you do that at home me and Daddy will let you start doing big girl things also." I have a 4 year age difference between my oldest 2 (all 3 of mine are girls) so this is something that really works in our household. Find something her brother gets to do that she REALLY likes...that is your "money" and "pay" her when she accomplishes what you want to "buy"!
On the same token, take responsibility for some of her accidents, like on a long trip, say, "I am sorry, that is mama's fault, we were in such a hurry, I forgot to let you do the rule [go to the bathroom before/after you leave and/or start an activity]
The other advise of letting her clean up after herself worked for us too. I went so far as to make her clean her cloths from start to finish, though. Not only put them in the laundry after cleaning after herself, but told her which button to turn on washer/dryer and fold and put the clothes up as well. It took 2 days of this (with a scowl on my face while she completed the tasks as to not make it fun). Of course there will be set backs and true accidents, but depending upon each individual circumstance, they will subside.