Hi, D.. Well, I don't know what other advice you got. Here are my thoughts.
First, what time are you picking up your daughter? If she is tired and hungry, that might be a reason why she always acts upset. Maybe you can see if the babysitter can give her a healthy snack before you pick her up. If that isn't possible, maybe you can greet her with a smoothie or an oatmeal cookie without too much sugar.
Also, since she's having a good time playing, she doesn't like to be interrupted. Even though she loves you and wants to be with you, she is forced to separate from her friends, the other child and the babysitter. If it's possible, maybe you can find a way for the three of you to spend a few minutes together before taking your daughter home; that way, she doesn't have to just get up and go home. Maybe a few minutes to make a transition between playing all day and going home to get ready for bed, will be a help to her.
Sometimes, kids really get angry with their parents when their relationship has no fun, no play, in it. She knows that it's all fun and play at the babysitter's, but Mom is all business (cooking dinner, going to bed). We find this in situations where a mom and dad are divorced; mom has to do all the hard, everyday business things like cooking, cleaning, helping with homework, disciplining, but dad gets to be the fun parent and play with the kids all weekend. Kids will naturally want to be with the "fun" parent and get angry with the "business" parent. In order to balance the situation, the parents have to make time for both fun and business with the kids.
In your case, your daughter might also be angry because, even though she likes being at the babysitter's house, you are gone all day. She misses you and doesn't understand why you have to go to work. And she's not going to be able to understand, at her age. Again, I think it's really important to fix that problem by making sure you give her enough fun attention when you are with your daughter. Give her something to look forward to when Mommy comes to pick her up.
I hope everything turns out just fine, and that this phase of your daughter's life passes soon.
Peace,
Syl