unlike men, women are wired differently.
we box everything in compartments. money, work, marriage

but for women, everything is connected.

firstly, she just had a baby, her emotions are all jumbled up

its not the amount of money, but what the significance is behind the giving.
negotiating with her like an employee is a bad move.
her complaint is that her collegues spouse put money into their purse when they see its empty. it could be anything from RM10-RM10000! the amount was not the issue but the thought of it that counts.

second, when you married her, did you have a thought in your mind that there will be another wife in the future? certainly not, right? if so, what is the issue with giving her 5k as she will be just keeping it if she is a good wife.

for the sake of your marriage relationship, you have to do the man thing.

buy her flowers, if she like them
apologise for not giving her an allowance before she asked
in other words, romance her la like you did before you married her.

and give her the allowance she asked for, say that you actually meant to invest it for the son, but she comes first (mean it la).

a marriage relationship is a dynamic one, it changes like the weather depending on the kinds of input you put into it.

all the best to you.