I do understand your concern
A lot of children will have these allergies and they eventually outgrow them, so there is no issue about these persisting for a significant time.
For the nappy rash
a. The best precaution is to avoid using the nappy. Instead, keep the area clean and dry and use only cotton underwear for your child. It may be a little messy. Do not apply powder after bathing the child. It would just make it worse. On the rash as such, you can apply vaseline jelly and nothing else
For the frequent cold
a. Try and identify what increases the symptoms. identifying and avoiding the "allergen" ( the thing that she is allergic to or the thing which increases her symptoms) is key
b. Also, keep a humidifier in the room. If you don't have one, boil a pan of water in the room to keep it moist.
I hope I have addressed your concerns