Is it permissible for a sister, who can only conceive through IVF, which is costly and physically exhausting, to undergo another IVF procedure to have a second child, knowing that her husband is well-off, or should she fear that she might be sinning due to the cost or hardship?

The legal rulings concerning the IVF or "test-tube babies" procedure have been previously clarified in Fatwa No. 32734. There is no sin in the high cost of the procedure as long as the husband is able to afford it and it does not affect any religious obligations. The assessment of high cost is relative to the financial ease or hardship of the one spending. As for the exhaustion resulting from the injections, there is no harm in it unless there is a certain damage. The husband is not permitted to compel his wife to undergo it, and it is preferable to perform Istikhara (prayer for guidance) regarding the matter.