If your life is harder/more stressful with her, then it is possibly the wrong thing for you at this moment in time.
I think there is definately that 'settling in' period when you need to adjust to the change in work/money and lifestyle and you are only a short way into that - also nights are getting dark, it is colder and that in itself makes everything look and feel a bit gloomy.
Personally, if you are only a few weeks in, I would hang in there for a short time. Can you get someone to share, maybe do a few days a week and pay you something towards riding?- if she is so good, maybe someone like a local mum who hasn't got time for her own and goes to the local riding school to ride? I pay someone £20 a week towards a horse and do her for three days, however, the owner never rides and I get to ride more often. It was costing me £17 an hour once a week at a riding school, so for me, it is a good deal and I get to mess about with horse of my own for a couple of days and ride out with dd.
DD (8) got her pony in June and like you, I did have a bit of a panic about what I had taken on, not money wise, but time wise - weekends I have to get back if we are out for the day to 'do' the pony. In the evenings, I have to think about going and getting her in, before tea (and she is only over the wall!). However, we have all got into a routine and if there is a night I can't make it, as long as the stable is done, the girl in the next box does it and I return the favour, letting out in the morning.
I would ask around and you may find someone who can help relieve that pressure. If she is such a good horse, it does seem a shame not to stick with it.
It wasn't until we got dd's pony that I realised how much I missed horses and just being around them. What do I love? The smell, the warmth, the fun, the chomp chomp as they eat their hay, riding out in the leaves, steamy grassy breath, crisp mornings in the yard, putting their warm rugs on in the evening and see them all clean and settled. Just everything!