Honestly, she's 3 and this is not a new situation. Not to downplay it, but my first thought is she's trying to get something. I have a 4yo dcg who's parents separated in November. Dad is busy buying her affection constantly, and she's now figured out that if she throws a fit, mom and dad will BOTH give her a treat or something special - dad because that's what he does to keep her liking him best, and mom because she feels guilty that dcg likes going to dad's more. It's ridiculous. One little tear at pickup will get promises of ice skating, ice cream at dinner, sleepovers at nana's house, the list goes on.

I've had to be quite firm with her, because she keeps on trying it with me. She'll whine that she wants Dad to pick her up when it's mom's turn, she'll argue with me about who is picking her up and wail that she misses her dad. Apparently she's trying it at school too (she is in JK). I tell her firmly once that either Dad will pick her up tonight, just like always, or that she'll see dad in a couple of days, but mom is picking her up tonight because mom misses her too. Then I ignore it. She pulls the same stunt about once a week, cries for 5 minutes, and then lets it go when she realizes she's not going to get anything out of me.

I could be completely off-base, but that's my first guess. She's old enough to understand the routine of going back and forth and it's been this way for a year, so I don't see how there could be anxiety over him actually not coming. It sounds like he consistently has her every other week, yes? Do you know if he spends time with her on his weeks when she is not at daycare? Or does he drop her with Grandma or something after daycare? I could somewhat understand it then, but if he's present and it's consistent I might try being firm and ignoring it, and see what happens. Good luck!