My son just went through all of that. He's 9 and had a cross bite and crowded teeth. He had to have the expander and braces and wears a head gear at night. He's managed through it wonderfully and only had his braces on for 6 months or so. He looks super cute now! My daughters probably gonna need something too...it's harder for girls.
Now, for me....when I was younger I had the expander, head gear, braces for 5 YEARS, major upper and lower jaw surgery which resulted in me being swollen for 6 months with my mouth wired shut for some of it...I was 15...it was mortifiying. I have 22 screws in my face and 2 metal plates...all because of an underbite. Now, I have developed a crossbite because of the surgery locking my jaw in. So, i have constitent headaches and riniging in my ears. I'm undergoing treatment for that right now. Way more information...the point is...I feel your daughter & MIL's pain!
Oh yeah, and the expander is way easier than it was when I was little. Now it's just a thing on the roof of the mouth that the orthodontist adjust every few weeks. Not bad at all. My sons mouth hurt for a day and then he forgot all about it.