Sorry to hear about your baby being so ill.
Have the doctors done any tests to check for parasites and worms? If not, may be it would be a good idea to get that done.
Make sure that areas in the house where your baby is touching and things that she puts in the mouth are clean. If she has soft toys that cannot be washed, put them into a plastic freezer bag and pop them into the freezer for a few hours, this will help to kill off any bugs.
Make sure that before she eats, you get her hands washed. Always wash your hands after touching her dirty nappy and after using the toilet and before preparing food. Keep uncooked meat separately to other foods to stop any contamination. Wash any fruit like grapes and plums before giving them to her to eat.
Make sure the baby is kept warm and out of any draughts. You can buy Vick especially for young children and you can apply this to her chest and back to help relieve any congestion. If she does have a fever, you can give her child medications that bring the fever down and also put on light clothing and apply a cool compress to her head. If she has a cough and a lot of congestion, you can also put a bowl of hot water with some Vick in her room, making sure that she cannot get to it because of the hot water. You can also purchase plug in vapour plugs specifically to help to relieve congestion.
When she is unwell, she will not feel like eating, but do make sure that she drinks plenty of juices and water. If she likes soup, then chicken soup is a good one to have when not feeling well. If he still has the diarhea, keep her off the milk for a few days - your doctor should be able to advise you with regard to that.
Children tend to get very ill when they are teething, so keep an eye on that to see if she is ill around her cutting a new tooth.
Because she has had such a lot of antibiotics, like newoutlook12 mentions, she may have a yeast infection. If she has a sore bottom this could be a yeast infection and the doctor would be able to prescribe a specific cream to treat that. If you notice she has any white marks or patches in her mouth that could be a yeast infection and the doctor would be able to prescribe a specific mouth gel for that.
Because your baby daughter has been so ill with these things, as a precaution, I would avoid taking her to any public places and not allow any visitors with colds and coughs to come into contact with her.
She could possibly have an inter ear infection sometimes the doctors can't tell if its really deep under the ear, have they checked? My daughter went through something similar and thats what it ended up being. Wishing you and your daughter the best hope u get this figured out asap. Watch out for signs of a yeast infection since she has been on so many antibiotics lately it can cause it to start.