There is no filter, just atomizer with coils inside and typically cotton for the wick. 6 is probably the nicotine level and is a good starting point. I have found most starter kits even for beginners discouraging in the fact that they usually suck.
Sounds to me like the PG/VG mix could possibly be wrong for that device and she burnt the coil, or wick. For that type of lower powered device you would want the lowest possible VG mix and also, Tam is correct some flavors or even brands can be harsher than others, when vaping at certain watts through curtain coils. Sometimes mixing a new flavor into rotation without changing the coil, especially if its a different PG/VG mix could lead to some adverse affects or flavors. For some more info on different types of E-liquid you might check out this blog post e-liquid-nic-salts-what-is-this-stuff?
Sometimes vaping can be tricky, and there are so many brands flooding the market, If you purchase the e-liquid at a vape shop be sure to tell them the device your vaping with and they should guide you in the right direction. If she is serious about quitting smoking with vape then this article is a good place to start: secrets-to-quit-smoking-cigarettes-with-vape-inside
I really want people to quit smoking with vape cause its fun, my opinion is that device and or coil set up might not be the best.