I used the modified save file like 10 pages back to get to the cowgirl scene for convenience sake. Just go to sleep and you'll see it.
To get the cowgirl scene, first pick the option to do lewd things with her at night but don't make her cum. When you end the scene, she'll ask you to keep going but pick the option to end the scene. She'll be in a bad mood the next morning and you'll have to raise it while not doing anything lewd for a week or until the next weekend hits. Taking baths together is fine, anything else probably won't work. Also helps to pop an aphrodisiac or have her sensitive for it to trigger.
I think there might be a bit of RNG involved since I tried a few times to get the scene with the same parameters and it would trigger only sometimes. Someone else can double check for me.
Can confirm cowgirl scene is in the game. These were the steps I followed to trigger it the first time so I think there is some RNG to it.
Don't do anything lewd for a few days and go to bed on the weekend with full vigor. Make sure that you've been keeping her mood at good or "<3 oniichan" for those few days where you don't do anything lewd. Then make sure her mood is at least good or "<3 oniichan" on either Friday or Saturday night. Have her drink an aphrodisiac and then choose to go to bed (you may or may not have to do this but it might increase the chances of it happening). You'll also have to have her trust and sexual interest really high.
Hope this helps all the people that have been asking.