I have stayed at All Star Sports and walked across the other two value resorts. The rooms are going to be the same in size but different theming, with not alot of difference between food courts, arcade, disney gift shop,etc., All three are going to make you feel like you are at Disney!
I did read the food court was a little bigger at Movies. Disney saw that after the first two were built the food court needed to be bigger. Don't know if that makes that much difference for me personally because we have stayed at Pop Century with a bigger Food court and All Star Sports smaller food court served the same purpose.
I have read that the bus service was better at All Star Sports , 2nd Music and worse at the Movies because of shared buses at times & that would be the order of picking up or droping off. I haven't experienced that or know if that matters. Seems like a filled bus is a filled bus. We have spent time waiting inline for buses, people with wheelchairs, no matter if it was at All Star Sports or Pop century (with own bus), or at Fort Wilderness, and people have waited on us with getting the strollers and children on board. Its just part of it!
I do remember that as soon as I saw the Music resort I immediately did not like the Rock inn section. I felt like it was more out in the parking lot. The section in the middle that overlooked the gardens and fountain & in between the two pools is probably where I would want to stay if I didn't request a room overlooking the big pool because it would be closer to lobby and would be handy to either pool. But it will not have the big disney characters in that section if that is what you want to see. I read somewhere it was the lovelier of the three resorts. Thats probably a good description of the garden area. If I stayed at music and wanted to see more disney I would ask for a room overlooking the big pool.
When I looked at the All star Movies & walked out the back of the lobby & saw the pool I remember telling my husband that this was my favorite, just because of Mickey standing over the pool, & it had Disney movie theming. But that being said, if your mom does not want to change, I don't think ones going to make a dime of a difference in your stay. I felt like I was at a Disney resort staying at the Sports and enjoyed the pool , foodcourt, disney gift shop, bus service, etc., I would think that music would even feel more that way! Hope you have a great vacation!