Your daughter might not get objectively easier to manage, but you will find her easier to manage as you gain confidence and expertise. What feels overwhelming now will one day feel familiar and doable. You'll know what she needs, how to respond and what isn't worth worrying about.
Our 13-year-old son is non-verbal, autistic and has learning disabilities. He's become objectively more challenging with every passing year, but we've become more skilled at meeting the challenge. We're able to meet his current needs better than we could meet his earlier ones because we've become more competent.
I should note, though, that his dad and I look after him 24/7; he's never attended school. I know other families whose children with similar needs leave for specialist school at the crack of dawn, come home late, and have help from social care at the weekends and holidays. Many of them haven't developed the expertise or confidence to care for their child, and it becomes much more difficult when they do have them. It doesn't get easier for them.
In my experience, the more parents try to hand the hard parts to others, the slower their learning curve becomes and the greater the chance their child will end up in full-time care. In that respect, support can become a vicious cycle. While it's a relief in the moment, over time, it can erode your skills and confidence to the extent that you don't believe you can care for your own child.
It's like hiking uphill with a heavy backpack. The slope might not get any easier - it may get steeper - but your legs will get stronger, and you'll learn which paths are worth taking. However, if you always hand your backpack to someone else, you'll never build the strength to carry it yourself. Then, when it's suddenly handed back, it feels just as overwhelming as it did at the start.
If you consistently do hard things, they eventually don't feel as hard.