Building up holiday

[girlsgirls20]

Really hoping someone can help me, I have tried looking online but cannot find much info.

I have been on maternity leave since July and I am due to return to work next month.
I am an employee on a zero hour contract but I usually do around 24 hours a week over 3 days. I had a meeting last week about returning to work and I asked my manager about putting in my accrued holiday at the end of my maternity leave so I would have longer off and she wasn't sure it would be possible. I have done this before in 2016 when I finished my maternity leave and I ended up having nearly 12 months off in total.
She seems to think that it is down to the employer to decide whether I can even accrue and take holiday built up during mat leave but surely as I've done it before it can be granted again?

If anyone knows about this or can attach a link for me to read, I would be very grateful.