$175 oil change

My mom has a 2008 Kia Rondo and it needed an oil change and a cabin air filter as it’s still under warranty she felt that she had to bring it to a dealer to have them change it as she needs to have proof that everything’s been done at proper intervals. But here’s where my issue lays. It cost her $175 for the labor and three parts. On top of that it took them an hour and a half to change the oil and cabin air filter. They said that it was because of the cabin filter that it took them so long. Personally I’ve never done a cabin air filter so I didn’t know how hard it was but I went out to look anyway. I know a common location for the cabin filter is behind the glove box so that’s where I looked. All it was, was a couple of clips and the glove box dropped down giving easy access to the filter. It took me less than 5 minuets to do this. Now factor in vacuuming the area round the filter, the oil change, and the other small stuff the dealer might do during this it should take at most 45 minuets. Now I work at an auto parts store and the most she would have spent is $60 on synthetic oil and the filter now list would probably be about $100. Is it seriously worth the $75 of labor for this or can she buy the parts and keep the receipts to show that she’s keeping up on the changes or would this void the warranty?