On average Kushina Habanero is 132 coupons/frag in events where you can spend coupons to get her. So, to get your remaining 46 frags will likely cost you ~6200 coupons. To get her to 4* and make her useful through breakthrough you will need ~13200 more coupons. So, ~20k in total. Her lowest ever event price is ~107 coupons/frag, but we haven't seen near that price since early Feb.