There is nothing in the law that forces you to accommodate this request; there are legal protections, however, that require you to accommodate breastfeeding in the workplace, such as allowing for breaks, providing a safe and secure place, etc.
Given the case as you have described it, what with the employee returning from mat leave early, it would seem like a very easy “give” to accept this 9 month WFH agreement – especially seeing as you are already hybrid.
You should consider the ergonomics of you employees home office, as well as potential privacy issues that could arise during Zoom calls, etc. If, say, you have a policy that all conference calls require employees to turn on their webcam, you may want to carve out some exceptions for this employee to protect her privacy.