She can use her own private key to do so.

So he would have to use his key after all.

When he didn't answer, she used her key and let herself inside.

So you might do something different, but you're using the same key.

She used her key from the inside and opened the door.

There was no need for me to use my key.

Use the most recent key if you're going to do that.

Or it's not clear what it is they have to go through to use their key.

He got there at 11:30 and used his own key to get in.

The security guard used his key and took me in.