Was it her abdomen, or the front of her? Her crop?
As for the mites, you'll want to retreat in less than a 2 week period. I do 10 days. Put dusting powder in all the bedding. You can mix the powder and water and 'paint' the water onto the walls as well, but mostly get it in the nesting area, etc. The eggs laid by the mites will hatch and you'll have the same issue again.
Probably not a good idea to squeeze the abdomen of a hen. She could be laying normally, or could be laying internally. (See the thread on this on these forums.) Just make sure she's getting good calcium and vitamin D and sunlight.
The mites might have caused the pasty vent (the dirty vent). I've seen that happen a lot. She'll be anemic, so I'd make sure all your birds get a good treatment with a probiotic laced mash. (Glenda heywood has an awesome recipe for one! Right here, in << >> marks, my additions in ( ) marks:
<< Give them the wet mash probiotic so they can make good gut flora. Use 1 qt of dry crumble feed, 2 qts of water. Do this: fix what amts to 2 tsp per chick per time mixed wet mash plus vit's.>>
<< NOW THE IMPORTANT INGREDIENT FOR EACH CHICK FED
and add 1- 1000 mg of Vit E by cutting the end off the vit E capsule for each chick fed this wet mash and 1 selenium tablet crushed for each chick fed this wet mash putting it in the wet mash. Use this for each chick your treating. So for each chick use 2 tsp of mixture and 1-1000 mg of Vit E and 1 selenium tablet crushed in the wet mash probiotic twice a day for them till the manure is solid. Feed each chick 2 tsp full of the wet mash probiotic and what they will clean up in 20-30 minutes. Then clean the wet feeders and restock with dry crumbles. Do this twice a day for a week till the chicks manure is right. Then quit the Vit E and selinium make just the wet mash probiotic. Then once a week for life.>>
For a good safe electrolyte and vitamin D boost, Glenda and I both recommend this:
<<2 tbsp of (organic) apple cider vinegar per gallon of the chicken water so their gut flora wil be regulated they should have this at least 3-5 days a week, then three days aweek after they are over coccidiosis (or other digestive upsets). The vit's are neccessary to clean up the damaged gut problem.>>
So, could you tell us what antibiotic (and why you treated?) By the way, treating with PRObiotics is absolutely essential after any round of antibiotics. Antibiotics kill good and bad bacteria indiscriminately. The bird's digestive system relies heavily on good bacteria. When the good bacteria colonies are compromised, you end up with pasty vent - such as you've seen in the bird. It just takes stress to throw off the bacteria, so during any time of stress (including parasites) give a probiotic boost at least weekly to prevent illness.
On the other hand, you do NOT want to use antibiotics ever unless there's a really strong indication that there's a bacterial infection and that the antibiotic is appropriate for that. Many of the bacterial products available and packaged for poultry are unfortunately very weak and ineffective. They're also wayyyyyy overly recommended by feedstore guys. THere are specific antibiotics you use for wounds, for digestive upsets, for certain types of respitatory illnesses, and they don't necessariliy work interchangably. Something to keep in mind. Misuse an antibiotic, and you might not be able to count on it ever again for use with that bird. Just a word of advice for all poultry owners - it's a common mistake.
