She needs to decide if she wants a removable battery mod , i think they are worth it especially if you want a very long lasting mod and not worry about replacing a built in battery type when it eventually dies.
A HUGE factor for me was cost , a great replaceable battery mod like the Sigelei can be had for a great price.
Add a quality charger which everyone typically goes with like the , Nitecore i2 , i4 , D2, D4 or the Efest LUC 2 or 4's can be had for around $20.00 and two quality batteries are usually in the $13.00 range thats the way i would go.
I am still using the replaceable battery mods i bought close to two years ago , all i do is recharge batteries now and then.