zuótiān wǒ gēn tā shuō wǒ bù néng qù.

In Chinese, time expressions typically come early in the sentence (often first) to set the time frame. Both are natural:

• 昨天我跟她说我不能去。
• 我昨天跟她说我不能去。 Putting time first slightly emphasizes the time as the topic, but the meaning is the same.

No. Chinese doesn’t mark tense; the time word 昨天 already places it in the past. Adding 了 after the verb highlights completion:

• Without: 昨天我跟她说我不能去。 (neutral past)
• With: 昨天我跟她说了我不能去。 (emphasizes the telling was completed) Don’t use experiential 过 with a definite time like 昨天 (see below).

The second 我 is the subject of the reported clause (what you said). It’s normal to repeat it. If the subject is obvious, you can omit it:

• 昨天我跟她说我不能去。 (explicit)
• 昨天我跟她说不能去。 (subject of the embedded clause understood as “I”)

Optional. With quotes:

• 昨天我跟她说：“我不能去。” Without quotes (very common): 昨天我跟她说我不能去。

Negation of modals goes before the modal:

• 不能 = cannot (ability/permission/possibility).
• 没能 = did not manage to (one-time outcome in the past). Examples:
• 昨天我跟她说我不能去。 (I can’t/am not allowed/it’s not possible to go.)
• 昨天我跟她说我没能去。 (I didn’t manage to go yesterday.)

Chinese chooses 来 (come) or 去 (go) based on direction relative to the speaker (or the perspective adopted in the sentence).

• If the event is away from the speaker: 去 (go).
• If it’s toward the speaker’s location: 来 (come). In reported speech, you usually keep your current perspective: if the event was “there,” 我不能去 fits. If talking to someone at the destination, you might say 我不能来 (“I can’t come”).

Generally no. 过 marks an indefinite past experience and normally doesn’t pair with a specific time like 昨天. Use:

• 我跟她说过我不能去。 (at some time before)
• Or with a count: 昨天我跟她说过一次我不能去。