Bravotan

Melissabar just my 2 cents worth and years of experience.

Watch her ingredients in her products. Remember petro chemicals, lauryl sulfates and pure oils can be a contributing factor of the fading off dirty or patchy.
if she is doing well the first week, it could be she is just more lax'd the rest of the 5 days or so and not applying a good extender 2 x a day.

If she is blotchy on the chest and under arm creases it could be a couple of things. Perfumes or shaving gels/creams to the under arms.

Medically, Does she take antihistamines? Benadryl, or OTC products to lessen allergy symptoms? Does she take an inhaler? Medicines that dry up the skin can contribute to the fading also..

How old may I ask is she?

If she is a teen she may have the hormonal issues that may make inconsistency in her spray tan?

there are so many factors, but if she is getting 10 days out of her spray tan that is great news, but the fading will occur different based on the type of products used prior to and after her spray tan. If she is using bar soaps such as curess, dial, coast, irish spring, tone, zest any antibacterial soaps this could be the major cause in "dirty uneven fade" tanning.
Body washes (GENTLE) is the best I have found to bathe with to maintain that spray tan. I personally use Aveda, Origins, Arbon'e, Breeze's Spa line body wash; great scents!, For the moisturizers: I use our own P.L moisturizer, Caltan's Breeze's Posh' line, Aveda REplenish,

These have worked great for our clients keep the skin cells lying flat to lessen the exfoliation process once you have the spray tan.
Best regards and good luck.

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