Supposing the surrogate mother gets too attached to the baby, what can be done to resolve the situation?

First Things first, it wasn't her baby in the first place, she was just a medium used to carry the baby.
There Are terms and conditions attached to surrogacy

You think it's a lip agreement?

In the developed countries, an agreement is an agreement..

If she decides to go against the agreement, the consequences might be huge..

However, in the less/underdeveloped countries anything goes.. She might go free if something like this should happen..

I believe things like this won't be done without any form of legal agreement signed.

It's too risky for only lip agreement

This is not possible because [assumption] the baby is taken away once born. There is no time for her to bond with the child. Legal agreements are also carried out beforehand to ensure nothing of the sort happens.
If such situation ever happened the public will have come across it because it is news [something out of the ordinary] and you wouldn't see the need to ask this question.
Another twist to the scenario is a situation where the baby is born deformed [blind, missing limbs or permanent physical scar], the baby is then abandoned by the legal 'parents' and left to the biological mother to raise.

For every surrogate, there are terms of agreement

Surrogates are being paid for the service and she knows the terms before acceptance

The issue of being attached to the child means she doesn't want to be paid and won't let the child go off her

Surrogate mothers are unknown till the dee day, they dont need to know your home or your family, you can meet her at an agreed guest house but agreement are signed before a lawyer and its binding once you have been paid after deliver