You never say "didn't has". It's simply wrong. When you use "didn't", the main verb doesn't change: "She didn't have to." In fact, for past tense verbs, there's no difference between I/you/we/they and he/she/it.

Prashant: This is one of the biggest mistakes made by learners. If you remember one easy rule, you will NEVER make this mistake again: After DO / DOES / DID you ALWAYS (no exceptions) use the BASE form of the verb (the infinitive with NO "to"): She DOES not HAVE to eat. He DID not HAVE to write. DID she HAVE to study? DOES he HAVE to drive?

Use "she didn't have to." It's the correct form of the conjugation of "to have". I have You have He/she has