A.M.
My oldest went thru it a bit at 2, it lasted a couple of months and then he was fine. When baby came he actually started getting more attached to dad, finally. :-)
My younger son is 2.5y and is doing this lately. I think it's partly feeling yucky from getting his huge back molars, and from introducing the idea of the potty, and we've been talking about preschool. Although now i'm remembering that he did it for no apparent reason a few months ago.
I will give him the extra attention while it's obvious he needs it, but with him I think the best way to handle things is to not deviate too much from the usual (or at least not for too long). For him, he needs to see that i'm still confident in what we're doing. If I reinforce that starting preschool IS something to be scared of then he'll be worse.
I'd say just drop the talk about baby for a bit, it is a very hard concept for toddlers to get (I don't think my husband or I "got" it before the first one lol). And if you feel like she needs the attention and you aren't getting resentful about giving it then give it, but with words like "do you need some extra cuddles?" rather than "what's wrong? are you okay?" kind of talk.
When it really wore on me that he wouldn't let me leave him, I just did so with people he knew and that knew him and who wouldn't be worried if went high drama. Then i'd come back sooner than usual and act like everything was fine because every thing was fine.
The best I can remember, they each went about 2 months with it.