FRN - hiya hun. I'm in total sympathy - my ds's are 3.5, 2 and 3 months and my 2 yr old (25 months) is a nightmare at the moment and sounds exactly like your dd. It's def her age I think - there was a thread the other day where someone else posted a question like yours and everyone piled on to join the 'terrible twos club'!
I find it really hard to work out the triggers for ds2 as well - sometimes it's a mystery to me. On Monday morning he quite happily helped to make his cereal, quite happily skipped to the table to eat, quite happily got up on his chair, I put the bowl down in front of him and before I knew it he was off on one! I kid you not, this was at 8am and it was 9.15 before it ended. Then it stopped for about 10 mins and kicked off again! I was in tears before 9am that day and the whole day just went from bad to worse as I was stuck in all day with the 3 of them (piece of piss for us SAHM though eh?).
Anyway - I really do find that ignoring is the best tactic, or sometimes if I cuddle him he will calm down but other times that just inflames him more so it's very hit and miss. The last few days, I've made a concerted effort to slow down round the house so rather than saying 'hang on a minute I'll just do this', I stop to give him that full on attention for those 5 mins if at all possible. I'll let him sit on my lap for a bit and then he'll have had enough, get down to play and I get on with something again (usually loading the washing machine or tumbler - you know how it is!).
He really doesn't lack attention at all - I'm always doing his jigsaws with him (he's obsessed) and reading books, talking to him, practicing counting etc, but if he wants attention, he wants it now!
He is also quite sensitive so say if he and ds1 are running from the kitchen to the lounge, if ds1 overtakes him he freaks out! Or if he wants to get in the car first and I don't realise so put ds1 in first....loads of bizarre things!
I've rambled long enough but basically, it sounds to me that what you are doing is right and it's just not practical to drop everything to do things for them all the time, and I'm sure it's a phase (groan!) that she'll grow out of.
DS1 never stropped in this way - ds2 just has a different personality!