Widening pants

Hi,
up until now, I’ve only ever had to take my pants in, and that’s always been a lot of work—meaning:
first remove the waistband, then open the side seams and sew them tighter, but then the waistband is too long again and has to be shortened, and so on and so forth...
Now my best friend Ella has asked me to make her pants wider, since she’s been gaining weight steadily lately...

How do I do that? Where should I get the fabric from? I’ve already opened up a pair of jeans, and in that case, just opening the outer seam was enough, so I have enough fabric available there. But it’s not like that with non-denim pants—here I’ll have to sew in extra fabric. How can I do that? Does the fabric have to be a wedge, since the legs haven’t gotten proportionally wider?

I’m asking for your help

Yvonne

Maybe a wedge in the center back or one on each side next to the pants pockets?
You’ll probably have to buy some fabric.

How's it going with the trousers?