My friend likes to feel walls?

So, a fairly new friend of mine seems to be obsessed with feeling walls.

I started noticing in the past 3 months as we've been hanging out more. She came over to my house and we were eating lunch at the table. I excused myself to use the bathroom and when I got back she was feeling the wall. She stopped immediately when she saw me and was instantly embarrassed. I asked her why she did that and she just ignored my question. We continued eating and then she went home.

The next time, we were at a restaurant and we both used the bathroom after our meal. I was in the stall and I legitimately saw her feeling the fall through the crack in my stall. She was actually moving both of her hands up and down the wall. I thought this one was disgusting because the walls weren't the cleanest and it confused me to bits.
When I flushed, she stopped and then I got out and I never mentioned it.

Another time when we were at her cousin's house for his birthday, we were in the other room watching TV and all of a sudden, from the corner of my eye, I see her moving her hands up and down the wall but this time from behind. I laughed, asked what she was doing and she stopped.

Now, just a week ago, when we were at her apartment and I was in the bathroom with the door open trying to get ready, I walked out and I see her with her face pressed up against the wall and she's moving her hands up and down it and looked like she was making out.

I walked over to her, asked her what she was doing and she told me she was kidding. I then asked again and got nothing from her. I hate how she won't tell me what is up with this strange habit.

IIN? What is this?