I would separate her...unless they are newborns a 20L is too small for all those dragons. Having that many dragons together will stress them out - and also will make it hard for each dragon to get the adequate basking time that they need. Uusally the more dominant dragon(s) will get the basking time and will thrive - while the others do not.
Her appetite is very low if she is only eating 3 crickets a day. This is probably due to stress.
I would separate her into her own tank (and ideally, for the health of the dragons - separate them all) and give her a couple stress free days to relax, then offer food again.
Try offering different feeders too - silkworms, roaches etc.
Also, once she is separated i would have a fecal sample checked as beardies will often get parasites when they are stressed - a coccidia or pinworm (or any parasite) overload would also lead to decreased appetite.
Bear in mind that if you choose not to separate the dragons now, that you should separate them soon. Do you know the sexes of all the dragons? If you do not - then they need to be housed separately until you know for sure because if you have multiple males they will start to fight as soon as they mature (likely, before you are able to tell the sex) or if you have a male and female(s)they will start breeding before they are fully mature and this is dangerous to your female. The dragons will ultimately fare better, especially at this critical growing period - if housed individually.
-----
1.1 Bearded Dragons
2.2 Leopard Geckos
1.0 Uromastyx (Mali)
1.1 Corn snakes
0.1 Mexican Black Kingsnake
1.0 Bairds Ratsnake
1.0 Rosy Boa
1.1 Green Anoles
1.1 House Geckos
0.0.2 Flying Geckos
0.0.1 Red Eye Tree Frog