Here is an experiment I'm conducting.
When I fostered a kitty previously, using a gate to gradually introduce him to
Cassandra, my reigning kitty, worked beautifully. It took patience and time but by slowly widening their area of contact with each other, they were able to co-exist and even hung out together. However, Autumn, who is still just a kitten really, is very feisty and knocks over and jumps over any kind of gate I could find. Plus, Cassandra is terrified of her, to such an extent that we've had bad accidents. And Autumn isn't helping in that she continues to bolt towards Cassandra any time they are near each other.
Above: Autumn peers through a gate slat.
Pet gates don't come tall enough for Autumn to not jump over or knock over. I am amazed that they don't. So I tried calling screen door companies, sliding window screen installers and outdoor pet haven places but got almost nowhere. I finally went to Home Depot and got this lattice material and had a local construction guy make the frame, secure it with hinges and a latch and it's basically a taller gate. Only problem is I can't move it from place to place, which would work better.
Good news is that Autumn now has more room in which to hang out. Bad news is that Cassandra still wants nothing to do with her and isn't doing the curious approaching I had hoped for. We'll see how it goes over time.
Above: Gate set up to acclimate two kitties. Cost: $120 including installation vs. $300–500+ for the potential screen doors that needed pet-proof screening and more work.