Looks like you are getting plenty of great ideas, but here are my two cents.
First things first, you have to know that are (or even CAN) train the glutes. Muscles don’t really work in isolation, and since the body is very responsive to demand it will find a way to perform movement. Now that doesn’t mean that when you asking your hips to into extension, that your glutes will do the work that they are supposed to, it just means that if the length tension relationships are off, maybe even you will end up using more erector spinae to compensate, for instance. This is a phenomenon called synergistic dominance, and is set up by one or more muscles within a group which is much more active than another. So that’s the bad news.
The good news is that you can do something about. If I were you I would try a couple quick assessments to help determine if joints are out if alignment and creating dysfunction thus creating pain.
Now, this gives you a place to start. With an anterior tilt as a default posture, it will be hard for the client to use the glutes the correct way. I would suggest taking a few sessions and really try to influence hop flexor and hamstring flexibility. Our job is to try and pull the pelvis back to neutral.
Hope that this helps
Try to determine if your client has an anterior pelvic tilt. This is easily done by looking at their waist band. If it tilts forward, you’re next step is to put put them up against the wall in and see you can
slide your hand in the small of their back. If you can do that you are looking at a forward pelvic tilt.