Offering one's own telekinesis is akin to dividing divine consciousness.
The impacts on aspects like Qi Shu aren't worth mentioning, as they can be compensated for. However, the potential exposure of one's thinking patterns and cultivation technique foundation to others is already a significant flaw.
Especially if it falls into Manjusri's hands, who excels in the Summoning Technique, that "potential" can be completely omitted.
Guanyin previously agreed to share her telekinesis because the subject was the Tathagata Fruit, and the person being helped was Jiang Liuguang, someone just starting to dabble in the Summoning Technique.
Jiang Liuguang himself hadn't even achieved Dharma Manifestation, so Guanyin's telekinesis was at most a one-time energy source to enable the Tathagata Fruit to suppress Jiang Liuguang's wounds.
If it were Manjusri, no matter how bleak the situation or how much it was discussed, Guanyin would never take such action.