First thing I'll say is GOOD ON YOU for wanting to work through the issue without 'bandaids'. Of course, you can always create a quick fix by throwing a market harborough or a martingale on her to pull her head down, and she'll look 'pretty' but in the end, the underlying problem as to why she is hollow will always remain and with her head strapped down, she'll find another way to resist and you'll wind up in an endless circle of strapping the next greatest gadget to her to get all her escape routes into line. You may as well wrap the horse in plastic and put it on wheels if you're going to go down that path
A video, or even just some good photo's would be hugely benificial to allow us to help you out with solutions. There could be a variety of reasons that she is star gazing, it would take multitudes of pages to describe each one in detail and give you some solutions to work through.
So for now I'll throw some basic ideas out there for you have have a go with.
First and foremost is the obvious one that everyone will say/. Get her saddle checked out, her teeth, make sure her bit isn't pinching her mouth etc. etc. etc. Just make sure she's got a clean bill of health with perfectly fitting tack. Ill fitting tack or a muscle out of place can create enough tension for her to hollow and stick her head in the air.
Secondly, I don't know how you ride but the most common cause of hollowing and 'star gazing' is that the rider is not asking the horse to go forward and push off it's hind legs into a steady hand.
So look at your position. Are you able to freely move your hands, your legs and your seat individually? You want all of your body to remain under your control, your hands should not move an inch unless you tell them too, your legs should not grip and wobble, you're core muscles/torso should remain upright and quiet, not pushing/pumping, and your head should remain perfectly balanced on your shoulders without 'nodding'.
Can you put your leg on and get a bigger trot without grabbing with your hands? Can you post, or even sit trot without your hands bouncing? If your hands are bouncing in time to the trot, you will be gobbing the horse in the mouth at every stride, so understandably he/she will throw it's head up and hollow to avoid the constant jabbing discomfort in their mouth.
Should you have ANY of these problems, I would highly recommend that you get some lessons on the lunge on a quiet school horse. Take your stirrups and reins away and try to do this a few times a week until you have found your centre of balance and don't feel the need to rely on gripping legs and pulling reins to balance yourself. A horse cannot remain in balance if the rider is not balanced his/herself.
moving on from your position to how you ride.
Do you ask the hind legs to swing under Razz's body each stride? Does she move immediately away from your leg when you put it on lightly? Can you ride a 20m circle without having to pull her in the shape with the reins? Unless you can do these things I am 99% sure that your horse is not going forward. Her hind hooves need to step into the front hoof print, or get very close to the print depending on the conformational limitations of your horse (again, photo's would be very usefull).
To get forwardness, you first need responsiveness. Go from halt-walk with a light leg aid. If she does not react, flick her with the whip. She may leap forward but do NOT touch her mouth when she leaps. She has gone forward from the aid so you do not want to punish her in the mouth (this is where your position, balance and effectiveness as a rider comes into the equation). Ask again lightly with the leg and expect that she will walk straight off. She should move up a pace or lengthen her stride within a pace from a small squeeze of the leg EVERY time. Downard transitions need to be equally as responsive. Put a light leg on, sit deep and ask her to come back. If she doesn't, sit back and give her a quick 'jab' of the reins. She needs to understand that if she doesn't listen to an initial aid then the result will be discomfort.
Once she reacts positively to you basic stop and go aids, the most important thing is to get her forward and engaged. You have no steering, no control, unless the horse is motoring off their hind legs. Otherwise you are trying to drive a front wheel drive Barina down a muddy windy four wheel driving track
I recommend that you go and have a look in the dressage section/ We have recently had quite a few questions in there regarding engagement and getting a horse 'on the bit'. Go and have a look in any post that has something to do with 'frame' 'on the bit' 'forwardness' etc. There are many great responses that will help greatly with improving your own horse.
I am lazy and just don't want to write the whole concept out for the 10th time