If your German chocolate and other liquids are making her cough, it isn't tobacco harshness, it is probably one of these causing the coughing:
Is she trying to direct draw in the vapor? Have her hold the vapor in her mouth for a moment and only take small slow vapes and open her mough to allow air in with the vapor. Some people try to vape like they smoked. I never did a direct draw like that when I smoked, but tried it once on my e-cig. About did me in coughing. Very harsh.
Vapor is very drying (from the PG/VG). It can take a few weeks to get used to it. She needs to keep lots of water going while she vapes, and perhaps some cough drops. If coughing continues past a few weeks try a process of elimination for the rest of the list.
PG or VG allergy. Try her on just VG without nicotine (no flavoring, just have her vape it alone in a clean atomizer that you've primed with VG). If she does fine, add some nicotine liquid to it (no PG). If she still is fine, it was the PG. If not try eliminating the VG totally with the same process.
If she is on certain medications, it can cause coughing, and vaping seems to make it worse. Blood Pressure meds can do this. She may get used to it.
If she has allergies, a post nasal drip seems to play havoc with vapor and can cause coughing. Saline nasal sprays can help and allergy medications over the counter. Consult your doctor.
It can be an allergy to the flavoring chemicals. A bit tougher to deal with. My buddy can only vape certain vendors liquids. No LorAnn's, No Capella flavorings, no vendors that mix "in house" with extract flavoring (TastyVapor, MyFreedomSmokes, etc.). Dekang's change in flavorings put her out of their products 6 months or more ago... so no Dekang liquids. All of Vapor Station's India made juice works fine for her though. She has no clue why. If it is flavoring, plain PG and/or VG with nicotine should be fine to vape.
Some have said certain atomizer models made them cough, or that when they tried a new atomizer, it stopped. Odd, but who knows. Are you both using the same model? Might want to try a 901 with stock battery or something different than what you are using now.
http://www.e-cigarette-forum.com/fo...hing-stopped-when-njoy-replaced-atomizer.html
Good luck to you both.