K.L.
Are you talking the difference between a soft nippled bottle and a sippy cup? Did your doctor say she needed to get off the soft nipple for dental reasons? Does she use a pacifier? According to the WHO (World health organization), the minimum that babies/toddlers should nurse for the health of child AND Mom, is 2 years -minimum. Up to 5 years is seen as normal. Your girl has a strong urge to suckle still. I know it is usually seen as bad to change tactics in midstream but I think flexible parenting is best for all involved. She's telling you she needs to suck. I would be interested to see if you can address that first. And then worry about her milk intake. My boy is 2.5 and nurses briefly just twice a day. He just recently decided to have any interest in milk what so ever. My doctors haven't been concerned about this. Good fats are definitely great for kids in many ways but especially brain function. There are several fish oil supplements for kids that are chewable. Introducing those and using olive oils in cooking instead of butter. And offering avocados. This should ease any deficiencies of milk fat.
Much of parenting is having a plan but listening also to the input our kids have and changing that plan to suite us all better. Relax. You can't force her to eat anything so just keep offering healthy things and she'll pick what she needs the most at the moment. Best of wishes.