If your daughter will be 9 months old in January, she must be 4 months old now. You will be weaning her around 7 or 8 months and presumably can delay your return to work until she is 12 months old. By then, you she will have been through all sorts of changes, sitting, standIng, crawling, trying first foods and she will no longer need breastfeeding anywhere near as frequently asked she does now. When I went back to work at 9 months my milk and bottle refuser fed morning and evening only. The rest we worked hard are ensuring she got through her dairy and gluten free diet but she was OK.
If you have only been on maternity meaney for 4 months then presumably you haven't received a huge proportion of the enhanced pay so far.... and as someone else said.. presumably this has been worked into the decision to move (I say gently as I suspect it might be something like a non optional army move with no extra pay...). You could choose to resign at the end of your statutory period instead and not take the enhanced pay or you could save the enhanced pay and just pay it back
Nursery at £60 per day for 5 weeks comes to £1,500 so less than you would have to repay. But maybe being 2 hours away would be too difficult unless you still have a home in the old location. However you could possibly get an emergency short term nanny.
Don't assume you can't go back to work because your 4 month old needs you intensely now. This will change which is why women fought hard to have maternity rights extended to 12 months leave. But it is hard to find part time work if you move locations.
You do need your partner to factor you and your daughter into his decisions... job location, where you live. Maybe you could even carry on working part time after the 12 months if you lived half way between the two locations and had a nanny for your daughter so she doesn't have to commute.
You will find a way.. between the three of you. I will never forget the horror of having an allergic high needs baby. We did work it out and things did get better. You have time to find a workable solution. I wish you the best.
And in answer to your question. . unpaid parental leave is at the employers discretion so this moght not be granted, you would have to consult your employers policies to see if this would civer the requirement to 'work' for five weeks.
You also mentioned holiday pay... you are entitled to 5.6 weeks of annual leave if you take a full year of maternity leave... you might be able to take this when you finish your maternity leave. You will need to consult your employers policy regarding whether this can be used as your notice period.
Another option is for you to transfer some of your entitlement to your partner under Shared Parental Leave so that he can take care of your child while you work these five weeks.