It’s good to go ahead and get them and get her used to wearing something, too.
I was thinking the same, she might not jump over onto stairs, especially if she is not used to going upstairs. At first I thought the same, why not just leave her out? But it sounds like she has some pretty bad anxiety. You don’t want her going through a window if she is really wound up and trying to get to you. Or hurting herself (or your house) digging out or tearing up walls/doors. If she’s better in her crate, I would leave her in her crate. 🤷♀️ Phoebe is penned for up to 7-8 hours (with breaks) every weekday. I did get a top for the pen, and it’s covered, so really it’s like a 4x4 crate, which works better with her need to sprawl than her 48” crate that she bangs around in. She chews and naps, much like she would be doing in downtime if she wasn’t penned.Jumping out of a pen on a flat surface and jumping a gate onto a staircase or landing are pretty different. If you haven't tried a gate for the stairs, it might be worth a shot. We have a gate blocking the upstairs staircase (it's on the first landing, so its elevated 2 steps from the main floor), and for the basement stairs we just have a low wooden board (about a foot wide) that leans against the entryway. Oona won't jump that even though she easily could, because on the other side are 4 descending steps to a short landing. I don't know the layout of your place so maybe this is all meaningless but I thought I would share. Maybe you can make the location of the gate(s) unappealing to jump over or maybe the stairs do that naturally.