I just took my boy of 10 months to Phuket last month 4 days 3 nights. I brought a small tin of formula 400g and estimate about 4 diaper change a day. In the end, 400g is just enough down to the last bottle of his feeds on our plane back to SG and I had to buy a small pack of diapers there cos not enough.
Getting diapers in TW shouldn't be a problem. But if you are concern on the type of formula available there, you may want to bring your own. To save space and depending on the type of FM you are giving your baby, you can get those packet form rather than tin. But I would think that most major brands of FM would be available so you would not need to bring too much.
You may want to pack in medicine kit just for your ger, toys/books to play on the plane. Est 1 - 2 outfits per day unless you intend to launder the clothes. Let her have some water or her pacific during plane take off to reduce the pressure to prevent ear pain.