If your fish had ich in the main tank, you need to treat the main tank as well. Ich is a free-floating parasite, this means it's in the water, not just on your fish. Ich medicine only kills it at one stage of life, so it's likely you'll have to use repeat dosages, which isn't healthy for your fish. The best thing to do is use a salt treatment and raise the temperature.
"
The first, safest and in the authors opinion best treatment method is simply salt. You don’t need any special salt just so long as it’s NaCI salt and not something like Epsom salt or marine tank salt. If you’re not sure just purchase some aquarium salt from your fish store. The method for treating is relatively easy. The common recommended dose for treating ich is 2 tsp per gallon of water. It’s not recommended to put the salt right in the tank. You should mix it in with water so that it dissolves and then add the salt water into the tank. I recommend that you add about a quarter of the salt mix every few hours so that you don’t shock your fish as badly. You only do this once not everyday like with other ich medications. Salt does not evaporate or dilute over time in the water. The ich will probably look like it is getting worse for the first few days while you’re waiting for the salt to have its effect on in. If the ich does not look like its getting better after 5 days you will want to increase the dose by another 1 tsp per gallon. If you are keeping tropical fish I would recommend slowly turning the heat up to 86 degrees to help quicken the life cycle of the cyst which will not be affected by the salt. If you are keeping goldfish or other cool water species I would go to 74-76 degrees. Some people will tell you that 80 is ok for cool water but this really brings them undo stress. 74-76 will speed up the cycle of the organism enough that it should be killed off out in a week’s time. Remember heat is not necessary to kill ich the salt or medication will do it on there own but increasing the temperature will quicken the life cycle of the ich organism. If you keep any invertebrates or very fragile species you may want to consult an expert of the species to make sure that salt will not harm them. I would wait about seven days before doing another water change so that the salt has time to wipe out the life cycle of the organism. When you are done treating for ich I wouldn’t worry about doing a massive water change just your normal maintenance and the salt will be diluted out over time. Once you do a water change it is not necessary to add more salt back to the tank. If you do a water change during your treatment or want to continue treatment after seven day’s you will need to measure out how many gallons you take out of tank. Once you have removed the amount of water that you feel is sufficient for your water change refill the aquarium with fresh water equal to what you removed in old water. Then re-dose the tank with salt equal to 2 tsp per gallon of water that you removed. For example if you removed 20 gallons of water then you will want to add 40 tsp. of salt back into the tank."
EDIT: Just because you can't SEE ich doesn't mean it isn't on her! Don't move her into the main tank until you do a full salt/temp treatment!