I say to use Desitin Overnight (we like the "creamy") every night before bed. Some would say to use something with every diaper change, but I think that's overkill and I never wanted that stuff on my hands so many times during the day. We tried every cream in the book (Burt's Bees, Boudreaux's Buttpaste, Aquaphor,the special kind the pharmacist mixes up, some natural stuff bought online, etc.). We liked the overnight Desitin the best. My son had a persistent rash (from 1yo-2yo) that lasted for about a year and then just went away (it didn't bother him much).
Oh, and with the sippy cup, I'd start trying her with it now. I had mine fully transitioned by 13 months, but I started probably around 9 or 10 months. I think it's best to do it slow and gradually. Just try her with it everyday. Mine took to water in it before he took to the milk, but he eventually accepted the milk. I never gave my son juice until about 2.5yo, by the way, and even now at 3.5, he only gets about 1/4-1/3 juice and the rest water.