Boy I know that feeling! I was in Vegas last summer with a bunch of people (hot hot HOT) but I refused to get into a pool when they all were around.
The main reason your 70 year old mum has lost at the same rate as you (I'm assuming here) is that you're building muscle at the same time as losing fat; whereas she's just losing fat. Body fat is lighter than muscle by volume.
Building muscle while losing fat is better for your health moreso than just losing fat, so what you're doing is a good thing. And many studies show that the more muscle you have on your body, the more calories you'll burn every day just maintaining it. However! Personal trainers are expennnnnnsive! If you've been with one for 3 times a week now since November, you're probably quite comfortable with the gym you're going to and know the routines fairly well. I would imagine that by now, you could get just as much of a workout without a trainer as you do with as long as you continue to push yourself and add more weight or make the cardio workouts more intense as you continue to get stronger and leaner.
Granted personal trainers can be a great wealth of information and inspiration, so hiring one for a session even once a month could keep you on track if you need that. If your gym offers classes, try taking one. The instructors I have had are great about answering questions before and after class as well. You could even talk to your trainer about what classes would be good for your ability range.
Anyway, what you're doing is great
I'm doing the diet & exercise too and each day in itself can be a challenge to make good decisions but I find it is getting easier. Some days I am dying for a cookie, but there are other days where I just can't wait to go to the gym.
Best of luck in your journey!