There are several metal trash cans available for indoor use. This one is from Simple Human:

but there are many similar cans available. My mom, who recently passed away, spent several years losing the battle with incontinence. She was so embarrassed, but I told her it was just one of those things that happens in later life, especially if you've had 5 kids. A new trash can is a small price.

This is just a thought. I used a diaper genie with my kids and it worked great. No smell ever and easy to dispose of. No sure how it would work with the pads.

That Simple Human one looks as though it is also lined with plastic; I can't tell for sure. There are always those outdoor galvanized steel ones; not something you'd keep in the kitchen (well, you could though...). They probably come in small sizes.

The best advice I have is to tie up the used pads in plastic bags and take them to the outdoor trash every day. I used small metal step cans for disposable diapers and for cat litter. They had plastic inner cans, and even with always flushing diaper solids away and lining with plastic bags, I had to throw them away when diapers were finished and the cat was gone. We didn't have problems with odor from the cans day to day because of their lids and because we didn't leave things sitting in them for long, but the plastic liners still held enough odor that I didn't feel comfortable using them for anything else later on.

I used a big plastic trash can for the cloth diapers. Funny thing, I don't remember it smelling as much as the others, probably because solids did not go into it and the diapers didn't sit in there longer than one day (two at the very most).

Just remembered. When we visited my MIL with the kids while they were in diapers, we always took the diapers straight outside without using an indoor trash can at all. They make small plastic bags on a roll for this very purpose. (She doesn't have a covered indoor trash can.) It would be kind of a pain to do that for longer than a day or so, but maybe your MIL would be willing to use just plastic bags that you could take outside as needed. -- Or you know what, my little plastic trash can for under the prep sink was $3 at Walmart.

Although they are very expensive, the Vipp trash cans come with a removable aluminum liner that has handles on the inside. I use Vipp trash cans and they are worth it. Until you open the trash can, there is no way to know that there is something rotten in Denmark:-)

The aluminum trash liner can be taken outside and refreshed in the sun every so often.

Homepro01

There are some wilderness human waste disposal systems that include bags with powders to help neutralize odors and solidify any liquids. They're usually small packages that can easily be opened and closed (with the powder right inside the bag). They are made to be fully sealed so you can pack the waste out. Perhaps you could use something like this to enclose the pads before putting them in the waste can.

This one has a galvanized liner.

Here is a link that might be useful: Trash can

We bought one of the small steel cans at Target. It does have a plastic liner, but it's removable.