Canto 2 -
Ayodhyā-kāṇḍa
Chapter 8: The Conversation Between Kaikeyī and Mantharā
Text 2.8.6

लक्ष्मणो हि महेष्वासो रामं सर्वात्मना गतः।
शत्रुघ्नश्चापि भरतं काकुत्स्थं लक्ष्मणो यथा॥

lakṣmaṇo hi maheṣvāso rāmaṁ sarvātmanā gataḥ
śatrughnaś cāpi bharataṁ kākutsthaṁ lakṣmaṇo yathā

lakṣmaṇaḥ hi = Lakṣmaṇa; mahā-iṣvāsaḥ = the great archer; rāmam = to Rāma; sarva-ātmanā = fully; gataḥ = is subservient; śatrughnaḥ = Śatrughna; ca api = and; bharatam = [is surrendered] to Bharata; kākutstham = is to Kākutstha; lakṣmaṇaḥ = Lakṣmaṇa; yathā = just as.

The great archer Lakṣmaṇa is fully subservient to Rāma, and Śatrughna [is surrendered] to Bharata just as Lakṣmaṇa is to Kākutstha.

[Mantharā here insinuates that] though Lakṣmaṇa and Śatrughna share the right to the kingdom, because They are dependent, there is no question of Them being causes of Rāma’s fear.

Lakṣmaṇa was fully subservient to Rāma, that is, in mind, words and body. Therefore, Mantharā thought that Rāma was not afraid of Lakṣmaṇa, [that is, not afraid that He would take over the kingdom], and that because Śatrughna was fully subservient to Bharata, there was no separate reason for Rāma to be afraid of Śatrughna.

NOTE. Mantharā is simply unable to understand the reality pertaining to Lord Rāma because He is naturally covered by His internal potency:

nāhaṁ prakāśaḥ sarvasya yoga-māyā-samāvṛtaḥ
mūḍho ’yaṁ nābhijānāti loko mām ajam avyayam

“I am never manifest to the foolish and unintelligent. For them I am covered by My internal potency, and therefore they do not know that I am unborn and infallible.” (Bhagavad-gītā 7.25)

Therefore, Mantharā was blind to the transcendental truths regarding Lord Rāma, the Supreme Personality of Godhead.