Yes, this is true, mange is common in boxers. You should, however, have a veterinarian diagnose the problem and get you the medication and dosage for this pup. Ivermectin is generally safe, but if you overdose your pup, it can cause serious problems. You need to have her checked at the vet, and weighed.
I am doing this as an info request, so you do not have to pay for this answer. It is not legal for me to give you dosing information on a prescription medication for a pet that I have not seen nor diagnosed. I can only give advice. My advice is you need to work with a vet on this problem. Demodectic mange (red mange) can be very serious and needs to be monitored closely. If it worsens, and spreads to the entire body, this can be a horrible problem that can take many months to cure, if at all. How will you know if it is working? What if it doesn't work or what if your pup has a reaction to the medication?
For these reasons, I am recommending you take your pup to the vet, and get your advice there.
Best wishes
