My mare is very calm and mellow, she is much sweeter and saner than my gelding always. She just turned four, I started her in May of last year.
When I was ready to ride, I saddled like normal, lunged her while bitted up and worked on transitions from walk to jog to lope and back down both directions, then took her in a round pen and tightened the girth - I always keep it loose at first to minimize cinchiness and tighten as we go. Then (after a deep breath and quick prayer) put my foot in the stirrup, stepped up, reassured her while slightly over her, then swung my leg over her and sat down. Patted her, swung my leg back off and got down. Lots of praise. Repeated from both sides about a dozen times, then called it a day.
The next day repeated the above process just a couple times from both sides, then asked her to walk around the round pen. She had been ground driven so was familiar with the rein pressure and directions, she had been lunged so was familiar with the voice commands to move forward. We walked and stopped, I dismounted, got back on, walked, stopped, and turned all over the round pen.
The next day we added a jog. A week or so later when we both felt confident we added the canter.
The next few weeks we walked, jogged, cantered, bended, stopped, backed, and then went on a trail ride with a fearless gelding in a quiet park.
Your mare looks confident, and it seems she trusts you, I think you are doing a great job. I would work on the cinchiness issue, maybe try the little bit looser at first method, and correct with a spank on her shoulder or growl if she shows her displeasure at being tacked up... my mare did pinned her ears at first, but when she tried to move away or swung her head at me she got popped and was told "QUIT!" - now she accepts it as part of the price of getting three good meals a day, all the fresh water she can drink, a warm stall at night and lots of room to roam during the day as well as unconditional love :)
There is no passion to be found playing small - in settling for a life that is less than the one you are capable of living. - Nelson Mandela