How to babysit a baby with separation anxiety and what should I do??

Ok I'm 17 and I've been babysitting for a while now. The other day, I planned to babysit a baby on 5 different days, which seemed fine, but today, it didn't go very well. The baby was crying almost the whole 6 hours and I feel really bad because the dad was in the house working and he kept coming down to calm her down. I feel like I'm hardly doing anything for them and maybe it's not the best fit. I know I still have to babysit the rest of the days but how can I make it a little more bearable. I feel really guilty getting paid to hold a crying baby until the dad comes to the rescue. He probably has to take care of her just as much as if I wasn't there. I feel like they would cancel on me but they don't want to cancel on me last minutes because they're really nice. Also, I tried EVERYTHING but she kept on screaming. She's 7 months old btw.
Answers

Katherine W

Have her dad play peek-a-boo with her there, where he hides behind his hands and then shows his face again. Then after a few minutes, have him hide behind the doorframe and pop out continually, like "Here I am! Now I'm gone! Here I am!' Then have him make the periods he goes a little longer and a little longer. Over time, she'll get used to the idea that he goes away and comes back. This might require several sessions. You can also try playing with her while he's in the room, so she can see that he's nearby but that her focus is on you. And it's okay to say "This doesn't seem to be working, what do you think?"

zeno

Lessen how to calm it down by building a Relation with the kid. Read to it, play with It, walk it around outside, bring it toys to Play with. Build up your social skills. Make Funny faces with it. Etc etc

Sukrit

Give him freedom and let all be as it is. May all have freedom and truth.