Here is a solution. It is not what you were asking for, but it is one way to resolve your problem with minimum of hassle with land lady, or any risk that she might accidentally lose some of your mail, or look at it before you get it.
I suggest that you go to the post office, or to one of those mail box places, and get a post office box that is large enough to contain all your mail.
Then you file a change of address form with the post office to have all your mail go to the post office box, not to be mixed in with land lady mail arrangement.
The arrangement you have described is very unsatisfactory, but can be legal in some places.
The cost of the mail box may be a minor irritation, but this way you have your mail every time you go to the place to pick it up.
When you select the mail box, check very carefully what times and hours the place is open ... you want one where you can go any time you please and be able to access your post office box. If I was you, I would pikc one that is convenient to the route followed when commuting between home & work, so it is no big deal to stop there each day.