The best way to increase supply is to get her to feed more. What if you had a nice bath with her and let her come on and off, on have some quiet time in bed together before her day sleep.

It's normal for babies of her age to drop feeds, but its also normal for them to pick up feeding again before they turn two. By 20 months dd was asking for boobie all the time.

Can you use it as a comfort thing too...so when she's hurt or upset just offer a boob.

It's very unusual for babies under 18 months to self wean...but fluctuating feed times and lengths is part of feeding a toddler.

Don't doubt the boobs! I would also stop offering milk in a cup if you want her to feed from you. The more she drinks from other sources the less she drinks from you...unless you want to reduce feeds?