Irritating Arena Conflict - Any Advice?

There are four days of lessons at the barn. Most of the people who take lessons come in and ride school horses and are very, very beginners. Amy and Jen give lessons on Monday, Thursday, and Saturday.
A few weeks ago, Catherine added someone she knows named Kat to Sunday lessons. I have been jumping on Sunday's in the outside arena, and sometimes on Wed evenings. Last weekend, before I got there, Kat took down all my jumps. When I went out to ask her if I could put them back up, she told me NO. I looked surprised (because, to me, asking is a courtesy, not really asking permission) and she said "can you wait at least half an hour? My riders can't ride around your jumps.") and I said ok, but then her delicate rider who apparently can't steer at all got too hot and so they had to do the lesson inside.
So I left a note on the board that asked if instructors could post their lesson times 48 hours in advance, and that way Willig and I would ride different times and avoid the arena when lessons are going on. Jen and Amy wrote their lessons (as in, they just put down their huge blocks of time - what I meant was an actual list of lessons so I could see, for example, that there was an hour free from 2-3 on Saturday), but for Kat, it just says "Sunday."
So, since the show is next weekend, I planned to jump Willig again today. And again, she took down my jumps. So I put them back up (I couldn't find her), got Willig, brought him in, and then she walked by and said "I took down your jumps" and I said "Oh. I put them back up." and she looked really, really irritated and all huffily told the parents of the kid (a kid on a LEAD LINE, and if she can't LEAD a horse around jumps, then she's got problems) they had to ride inside.
Like 30 seconds after I finished jumping, she had the next rider take down all my jumps. She didn't ask, and didn't know that I wasn't going to ride another horse (which, normally, I ride Mercury over jumps after I ride Willig over them if I'm not too tired but today I was going on a trail ride with Sam).
So - I understand her position. She's a trainer, and she makes money giving lessons, and it is easier to ride in an empty arena. But my position is that I am there SEVEN days a week, while she is there ONE, and therefore, I have seniority, and if I want jumps in the arena, then I get jumps in the arena. I think baby riders who don't board a horse shouldn't get to control the arena all day four days a week, especially both weekend days.
And, I don't have problems on the other three lesson days. Only her day.
So one solution is I shift my jumping day to Saturday and avoid her completely.
Another solution is I talk to Catherine about what would work best for conflicts between boarder riding time and lesson time.
Another solution is I talk to her, but I actually don't think that one's going to be effective.
Another solution is I ride after lesson hours, but one thing I like about weekends is spending four hours out there in the middle of the day. It's not as fun from 6-10 pm which is what I do every weeknight.
The problem I see is that as we move into winter, everyone will want the inside arena, and it is too little for me to ride Willig in there with beginners who can't steer (especially with jumps), and I don't like having to ride after 7 pm on the weekends (lesson days go past 6 pm).
Any thoughts? I am being kind of selfish, and it is a problem kind of unique to me because no one else rides at my level (or jumps or has a horse as big as Willig).