Hello There!
Thank you for reaching out!
I am sorry to tell you your partner is right. English Ivies do stick their “feet” onto walls or whatever they climb on. I experienced this for myself! Like you intend to do, I used a few clear clips to train the stems up the wall. It works like a charm! However, with time, the English Ivy did anchor itself onto the wall! I had to remove these stems from the wall when I needed to repot the plant into a bigger pot, and those stems did leave their “feet” on the wall. They can be scraped off, but there is the risk of damaging your wall finish.
If you want to train a plant to climb in your bathroom by using clips, I recommend you select a different trailing plant, like a Heartleaf Philodendron or a Hoya Carnosa. Their stems are thin enough for those clips. Pothos are great climbers too, but their stems are too thick for those clips. You can also use other methods to fasten your plant’s stems into the window frame. Whatever you do, make sure you have the flexibility of removing the plant for maintenance purposes.