Your girl is old enough to be safely treated for ivermectin; lots of rescue babies are when at this stage when badly neglected pregnant and nursing mums with young babies come into rescue with all sorts of nasties and often advances cases.
The ivermectin dose and strength is tailored to the body weight. Your vet will treat with xeno 50 instead of xeno 450.
Please leave the judgment to your vet as to wether this is necessary or not. An advanced case of mange mites can do more damage (including a very slow and agonising death) than any xeno ever will, not to mention the pain and misery of an advanced untreated case.

Sometimes you can box yourself into a very small corner when you hover obsessively over your piggy and over-research because you can easily lose any sense of perspective and proportion.