Earlier quoted context omitted.
She didn't give a security guarantee. And even if she wanted she can't. Japan can't even sell arms to Taiwan right now. Even starting selling arms would be a huge change, let alone a mutual defensive pact. It's extremely hard to change the constitution of Japan. It's the only constitution that has never been revised since WWII. LDP has been pushing this agenda for decades and nothing really happened.
She just won a super majority in their legislature, she can even amend the constitution now.
The process to amend the constitution of Japan [0]:
1. two thirds of the house
2. two thirds of the senate
3. referendum
LDP just won the house. IF all LDP house representatives agreed with Takaichi then she could pass the first stage. Only two left!
[0]: https://ja.wikipedia.org/wiki/%E6%97%A5%E6%9C%AC%E5%9B%BD%E6...