Hi meandmine! First things first I think librarians have one of the most challenging positions (in a good school) because they are assisting teachers, creating your own unique lessons and themes, assisting students directly with their projects, research or recreation reading items and all for several different ages and an entire school! That on 1 - 2 people could really be taxing - just think of the number of students you interact with vs. the number a teacher interacts with! So know as you move from librarian to teacher that may easy some of the load at least you would be working with one (maybe two) grades!
I know there are a few single teacher mamas on the board, hopefully they will see this thread and chime in!!! That said I find
most teachers that I have met (married or not) struggle with the situation you describe especially at the beginning of their careers.
I'm student teaching and in college full-time to finish my BA and get my single subject credential
all while parenting completely solo! Like you, I also absolutely LOVE the work I'm doing, especially when I'm in the classroom.

The prep, paperwork & grading are not as much fun at this point while I'm still learning and striving to find my own groove. I have already made some decisions (based on advise given and my personal observations and goals) that I feel will help with work/life balance in my home as a solo mama.
1) I plan to teach in an independent school setting (ideally teaching in an independent girls' secondary school)! I decided standard public is not an option for my life as a solo mama even if it means less income.
I teach secondary English and with the local public school district there are 35-40 students per class and a full time load I believe is 5 classes which equals a ton of grading, not enough text, etc........while the school I am diligently working towards employment at has an average academic class size of 13 with a full time load being 4 classes for English and Science departments. Much better for work/life balance in my opinion!

In my area there are a fair amount of private and independent schools that pay quite nicely so it all depends on the school I get offered a position at...
2) I plan on my dd being enrolled in school close to my job! I saw on another board one teacher mama say the following about a school she applied for a teaching job at:
"I have a third grader one block down the street at the elementary school and I want to be close to him, so he can walk to my school after school. I want to make my room a place to go to learn and feel safe! If the high schoolers need to see me after school they can come see me and I don't have to worry about leaving to pick up my son!"
This really resonated with me! While my dd is young I could hire a student to go pick her up (most likely by car but possibly walking depending on the distance) and bring her back to the school so I can do my grading, advising clubs, etc.
A teacher mama on here has her son at the same school she works at, he goes to aftercare while she grades, preps, etc. She teaches ES so it works for them since I will be in secondary I will have to go with the above senario at best.
3) Seek wise council from those in your direct position. For me I found an online community of English teachers which has been a blessing in tips and tools for managing challenges that are particular to English teachers.