Buy the other 15 frags, she is more than worth those 1700-2000 coupons.

About her breakthroughs, depends the team you have in mind.

An example of a decent and not that expensive team for her is:

Haku edo tensei yagura edo tensei x

Earth main kushina x

X x x

Talents: 43122, summon: koh, summon mystery: giant katsuyu level 3.

It's enough her chase +1 to work perfectly fine.

(works also with water main, Talents: 3223X where X is 2 or 3 or 4 at your choice).