Sita's Superpowers

Citations are in the format (Kanda, Sarga, Verse) and refer to the Critical Edition of the Valmiki Ramayana. 

Assertiveness and political savvy

Sita was first and foremost, a Lady. This means that she was correct in etiquette and used courtesy as her armour, and it also means that she was essentially groomed to rule over people.

Albus Dumbledore said in Philosopher’s Stone, “It takes a great deal of courage to stand up to your enemies, but a great deal more to stand up to your friends.” And Sita’s authoritative and commanding personality is demonstrated against friends and enemies alike.

e.g. in (Ayodhya, 27, 3), Sita straight up taunts Rama, calling him a woman disguised as a man (स्त्रियं पुरुषविग्रहम्), because Rama refused to take her with him in exile. This would be thought a pretty big insult even in our times, but in the context of the Ramayana it was a very grievous insult, because the men of the Ramayana were simply obsessed with manliness (पौरुषं).

She also boldly advises Rama to not enter Dandaka (which he ignores, and therefore invites trouble), and her comeback to Rama in (Yuddha, 104) has to be heard to be believed. She also freely and generally orders Lakshmana about on multiple occasions.

And of course, there’s her multiple verbal beatdowns of Ravana. My favourite:

त्वं पुनर्जम्बुकः सिंहीं मामिहेच्छसि दुर्लभाम्

How can a jackal like you covet a lioness like me! (Aranya, 45, 32)

Sita's political savvy is also shown in at least two situations,

1. Her handling of her kidnapping and rescue - see my answer to Why did Hanuman not take Sita with him when he visited Lanka in search of her?
2. Her poise in when she was sneaked outside the city limits by Lakshmana and asked to stay with the rishis (she was not banished) in (Uttara, 47):
   
   यथा भ्रातृषु वर्तेथास्तथा पौरेषु नित्यदा |
   परमो ह्येष धर्मः स्यादेषा कीर्तिरनुत्तमा || ११||
   यत्त्वं पौरजनं राजन्धर्मेण समवाप्नुयाः |
   अहं तु नानुशोचामि स्वशरीरं नरर्षभ | यथापवादं पौराणां तथैव रघुनन्दन || १२||
   
   When the brothers and citizens face bad publicity such a move (separation/estrangement) is prescribed. O King (Lakshmana), when you receive (your share in the kingdom and) citizens in accordance with Dharma, (you will understand.) O bull among men, (for my part,) I will not emaciate myself over the insults I've received from Rama and the citizens.

Words cannot describe the awesomeness of this response.

Magical/Spiritual powers

In the Ramayana (and Mahabharata) universe, spiritual merit can be used to solve problems via various applications.

These applications form a hierarchy as shown in this chart:


Now in Sita's case, she was meritorious enough to use curses, and was able to invoke favours from Agni without external assistance.

In the first case. Sita put up a blade of grass in between herself and Ravana twice - once in (Aranya, 54, 1) and another in (Sundara, 19, 3). It is implied that this was her standard behaviour whenever Ravana came to threaten/tempt her in Lanka. In (Sundara, 20, 20) she informed Ravana that she was more than capable of cursing him to oblivion.

Given the usage of blades of grass as bearers/conductors of Astras in both epics, it is very likely that Sita was also planning to use the grass as conductors for her curses. Further, Ravana, despite having a track record of raping women, threatened to eat Sita rather than rape her. Given that he did not fear humans in general, the only explanation is that he took Sita's threat of cursing him fairly seriously.

[In (Aranya, 54, 19) Sita says that she does not wish to defend her body against imprisonment, injury and death. This is misinterpreted to point out that Sita was not willing to use a curse to defend herself. However in the last line of this verse Sita specifically says that she cannot tolerate dishonour - taken as a whole the verse means that "I do not care if you hurt my body but if you try to dishonour me I will not take it lying down."

Dr Pattanaik grievously misinterprets this same verse as "I am not my body. I will never ever be violated." Not only is this completely contrary to Sita's words, it is horrifically disrespectful to actual survivors of rape and abuse.]

In the second case, Sita invokes the favour of Agni so that fire did not hurt either Hanuman (Sundara, 51) or herself (Sundara, 53) and (Yuddha, 104-6). See also The episode with Agni and Sita. On a completely unrelated note, such invocation of favour from a devata/asura is a technically known as Theurgy.