This is the 8741st most frequent Japanese word.
替り
"替り" (kawari) means "substitute" or "replacement."
In this sentence, '替り' (as '代わり' is also written) means 'substitute' or 'replacement', indicating that the person did something in place of someone else.
彼女は替りに私の宿題を手伝ってくれました。
She helped me with my homework as a substitute.
'替り' in this usage refers to 'in exchange for' or 'at the expense of', showing a trade-off between two attributes.
この商品は品質の替りに値段が安いです。
This product is cheap at the expense of quality.
Here, '替りに' means 'in return for' or 'as an alternative', indicating a reciprocation or compensation.