Firstly - sand; children's playsand is fine, but remember the risks.
Food - it is highly unlikely that your dragon would have become impacted from eating too many crickets too quickly, more likely that impaction was caused by the substrate or too-large crickets, although next size up from pin-heads is fine for a dragon of that size. Unless our sizings work differently between countries
Crickets biting - I presume you're feeding black crickets? Well there are a few things you can do; 1)switch to browns, which tend to be less cannibalistic and aggressive, though they don't grow as large and are very quick little critters! 2)feed your dragon in a separate enclosure, or take the leftover crickets out so they don't bother her,. 3)feed less, and increase if she eats all that you put in, so there are none left in her tank. 4)Put a bowl of veg in there, which you should provide for the lizard anyway. The crickets will usually choose to eat the veg rather than bother the dragon, and become gut-loaded at the same time!
Although crickets can be bothersome to the dragon it is quite unusual for them just to bite her and cause bleeding.. if she has an open-wound you need to get a product like tamodine on it to stop it becoming infected and to speed up the healing process.
I am concerned about the breeder you bought your dragon from - he should not be selling Bearded Dragons so young. This is irresponsible practice and he should be advised to look after the hatchlings properly and to an adequate age before he sells them on.
Have you read the care sheet on here? -
Bearded dragon care
It is imperative you provide the right enclosure, etc, for your dragon. How are you housing her? - temps, UV, tank size, etc.? How often/much are you feeding her and on what?
I'm glad the vet sorted out your problem, and I hope your little one continues in good health
