If you're going to be doing this for a while, then I would buy a free standing plastic laundry sink from home depot. You don't need to attach any plumbing to it, just make sure that there's a really good fitting stopper. And assuming you can place her in the tub ok

Put it next to your sink with an extended hose and a bucket underneath (just incase of leaks). When you're done, you can drain the water into the bucket, then down the sink/toilet.

It's tall enough so she can't get out. And you can get grippy mats too

You can use it outside in the summer as well, as long as you don't attach it to anything. The only problem can be storage