Changing cat from indoor/outdoor to indoor only

I'm asking for my sister-in-law. My brother died a few months ago and she will be moving from their big house in the country to an apartment closer to where she works. She asked me for ideas on helping her 14 yr old cat make the change from going in and out the pet door at will, to being in an apartment all day. Sis sometimes works long hours depending on the current work assignment. The cat was feral when they found her many years ago and is a hunter at heart. She is used to catching and eating mice, etc. She is spayed and litter box trained. I told her to get the cat microchipped and put a collar with a plastic tag on it. The cat hadn't liked the metal tag clanging against a food dish, etc, so they didn't make her wear it. Now, obviously, she's going to have to, just in case she gets outside.

I am sure there must be more suggestions. Is this do-able? I hope so.