She nodded her assent ____ the proposal.

Assent to something:
English Meaning - To agree to or give official approval to something.
Bangla Meaning - সম্মত হওয়া।
Example Sentence - Eventually, the government assented to a modified version of the plan.

So, Complete Sentence - She nodded her assent to the proposal.

আরো কিছু Appropriate Prepositions,
Akin to - সদৃশ;
Allot to -বরাদ্দ;
Appetite for - ক্ষুধা।

Source:
1. Cambridge Dictionary.
2. Accessible Dictionary by Bangla Academy.