Is it permissible for a barren woman to use herbs that may help with conception, with the permission of Allah?

If the herbs you are using cause no harm, then there is no objection to treating yourself with them. Indeed, the Wise Lawgiver (Allah) has permitted, and even commanded, treatment, for the Prophet, peace and blessings be upon him, said: "Treat yourselves, O servants of Allah, for Allah has not created a disease but that He has also created a cure for it."