Is financial stability important? Yes.
Is it more important than emotional stability, and having a supportive, loving home? NO.
I’m over-simplifying, of course, but providing your daughter with a stable, loving home doesn’t just mean being mortgage-free by 40. (Some people live in rented accommodation their whole lives - would you say they’re letting their children down!?)
You're not failing her by being a single parent. Instead of obsessing over mortgage payments, focus on showing your daughter the strength that comes from being financially independent and not having to rely on another adult to survive, which would leave you very vulnerable and at more risk of emotional and financial abuse.
If later down the line you are tempted to live with a potential partner, think very very hard before moving them in, even if having 2 incomes in the house seems more advantageous for your child. It isn’t always. Gently, you need to change this mindset or you might become tempted in the future to sacrifice your emotional stability, or even your health, just for the sake of having more money coming in.
If you’re not on the breadline, and your job is in a fairly safe industry, you’re fine OP. Really!