I like Torben's list, but I don't think that having a child who is low on the growth curve is a reason to be overly concerned about weight loss unless your child has all ready been diagnosed as being underweight by his/her pediatrician or with failure to thrive. The reality, though, is that children in the lower percentiles follow the same growth patterns as children in the upper percentiles. I doubt anyone would bat an eye if a 26 pound 2-year-old lost two pounds. While it might seem alarming that your child has gone from the 25th percentile to the 10th percentile, a quick check for growth charts shows that the difference between those percentiles is, like, 2 pounds. What I'm saying is, it doesn't take much for a kid to fluctuate between percentiles at this age, and my daughter has floated between the 5th and 10th percentiles her whole life.
There does come a point in a child's development when their eating habits change because they are not growing/changing as rapidly as they previously were. I have found in my own kids and in my friends' kids that this usually occurs right about the time they turn two (some earlier, some later).
My daughter just turned 2 and could probably be awarded the crown for world's pickiest eater. She'll go a couple of weeks and pick around throughout the day with her food, then she'll suddenly gear up and start eating more. This usually coincides with a small growth spurt. After the growth spurt is over, she goes back to her usual routine of picky, less-than-stellar eating.
Frequently, I've seen that toddlers at this age lose some of their baby fat and grow taller. If she's grown taller, then there shouldn't really be need for concern. Her body is getting adequate nutrients to continue growing, it's just that the resources are being allocated differently (ie. growing in height rather than girth). Additionally, your child is more active than he/she has ever been, and, therefore, burning more calories as a result. You would think this would make your child hungrier and make them want to eat more, but it generally doesn't.
If she has not gotten taller, this should probably be cause for concern. There are plenty of illnesses and diseases whose early indications are so few or minor that it's not until the patient becomes seriously ill that they even go to the doctor. When it comes to weight loss like that, diabetes comes to mind as one example.
As for her crankiness, strangely enough being cranky or clingy is one of the signs of a growth spurt. So, perhaps she's just growing. Or maybe she's teething. Or maybe she's bored. Who knows? Kids get cranky/clingy for lots of reasons. If you don't believe she's ill, then the clingy list could go on and on.
She will probably pick her eating up again on her own. One night you'll sit down to dinner and she'll clean her plate and ask for more.
This next part is purely opinion, kindly remember I'm not a doctor--never have been; never claimed to be: I would give it maybe two to three more weeks (depending on your tolerance level) and see if she's improved any. Despite my daughter's eating issues, she's never gone more than a couple of weeks of being exceptionally picky. Anything more than that and you're starting to get to the 2-month threshold and that, personally, seems too long. I have been known to weigh my daughter frequently so there's no shame in standing her on the bathroom scale if it will give you some hard data to take with you to the doctor.